Mobile communication system enabling efficient use of small-zone base stations

ABSTRACT

A mobile communication system includes a plurality of radio base stations forming respective radio zones and a mobile station selecting a wait zone and a base station to which a request for a message channel is to be issued. Each of the plurality of radio base stations is assigned an order of priority. Information relating to the order of priority is used by the mobile station to select a wait zone and a base station to which a request for a message channel is to be issued.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional reissue application of and claimspriority to U.S. Ser. No. 11/008,757, which was filed on Dec. 9, 2004and which issued as U.S. Pat. No. RE42,326 on May 3, 2011. U.S. Ser. No.11/008,757 is a re-issue application of and claims priority to U.S.application Ser. No. 08/880,665 now U.S. Pat. No. 6,493,561 issued onDec. 10, 2002, and which claims priority to Japanese PatentApplication(s) JP 8-163330 filed on Jun. 24, 1996 and JP 9-155286 filedon Jun. 12, 1997. More than one reissue application has been filed forthe reissue of U.S. Pat. No. 6,493,561. The reissue applications are:Ser. No. 11/008,757 filed on Dec. 9, 2004; Ser. No. 11/398,460 filed onApr. 5, 2006; Ser. No. 12/702,435 filed on Feb. 9, 2010 (now abandoned);Ser. No. 12/783,778 filed on May 20, 2010; Ser. No. 12/847,426 filed onJul. 30, 2010 (the present application); and Ser. No. 12/847,469 filedon Jul. 30, 2010. Ser. No. 11/398,460 is a continuation reissueapplication of Ser. No. 11/008,757; and Ser. Nos. 12/702,435 (nowabandoned), 12/783,778, 12/847,426 (the present application), and12/847,469 are divisional reissue applications of Ser. No. 11/008,757.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to mobile communication systemsand mobile station apparatuses, and, more particularly, to a mobilecommunication system in which a radio zone where a mobile station is toenter a wait state is determined by the electric field intensity of areceived radio wave that arrives from a radio base station, and to amobile station apparatus that receives communication service byaccessing such a mobile communication system.

The present invention also relates to a mobile communication systemwherein a mobile station selects a base station to which a request for amessage channel is to be issued, based on announcement information fromthe base station.

2. Description of the Related Art

Recently, a variety of mobile stations including an automobile mobilestation and a portable mobile station access a mobile communicationsystem. With a competition between a plurality of carriers as abackground, the number of mobile stations is increasing.

A mobile communication system may have a large-zone construction inwhich a base station covers a relatively wide service area or asmall-zone construction in which a plurality of base stations cover aservice area.

In a mobile communication system, radio base stations operated on asmall transmission power and forming microcells or picocells areprovided at the center of a big city characterized by a particularlylarge volume of traffic so that a multilayer cell is formed.

Radio base stations operated on a small transmission power are alsoprovided in an underground passage and a tunnel in order to enlarge aradio zone sufficiently to eliminate a dead zone.

FIG. 1 shows a construction of a conventional mobile communicationsystem.

Referring to FIG. 1, radio base stations 61 ₁ and 61 ₂ form adjacentradio zones 62 ₁ and 62 ₂, respectively. In the radio zone 62 ₁, a radiobase station 61 ₃ forming a microcell 63 and a radio base station 61 ₄forming a picocell 64 are provided so as to form a multilayer. Mobilestations 65 ₁-65 _(N) are located movable in the radio zones 62 ₁ and 62₂, the microcell 63 and the picocell 64.

In the radio base station 61 ₁, an antenna 66 ₁ is connected to anantenna terminal of a transmission and reception unit 68 ₁ via a commonantenna equipment unit 67 ₁. A control terminal of the transmission andreception unit 68 ₁ is connected to an input and output terminal of abase station control device 69 ₁. A line terminal provided in thetransmission and reception unit 68 ₁ and a communication port of thebase station control device 69 ₁ are connected to a control station (notshown) via a transmission device 70 ₁ and a communication link 71 ₁.

Since the radio base stations 61 ₂-61 ₄ have the same construction asthe radio base station 61 ₁, the corresponding elements are designatedby using suffixes 2-4 in the description below, and the illustration anddescription thereof are omitted.

An antenna 72 ₁ of the mobile station 65 ₁, is connected to an antennaterminal of a transmission and reception unit 74 ₁ via a common antennaequipment unit 73 ₁. A modulated input and a demodulated output of thetransmission and reception unit 74 ₁ are connected to a microphone 75 ₁and a speaker 76 ₁, respectively. A control terminal of the transmissionand reception unit 74 ₁ is connected to a control terminal of a controlunit 77 ₁. An input and output terminal of the control unit 77 ₁ isconnected to a display and operation unit 78 ₁.

Since the construction of the mobile stations 65 ₂-65 ₁ is the same asthe mobile station 65 ₁, the corresponding elements are designated byusing suffixes 2-N in the description below, and the illustration anddescription thereof are omitted.

The base station control device 69 ₁ of the radio base station 61 ₁ inthe above-described mobile communication system is directed by a center(not shown) via the communication link 71 ₁ and the transmission device70 ₁ to generate announcement information including a wait enabled leveland a wait disabled level as shown in FIG. 2 and transmits theannouncement information to a predetermined control radio channel(hereinafter, simply referred to as a control channel) via thetransmission and reception unit 68 ₁, the antenna common equipment unit67 ₁ and the antenna 66 ₁.

In addition to the wait enabled level and the wait disabled level, theannouncement information also includes a message type identifyingtransmitted information as the announcement information, a mobilestation transmission power specification specifying a transmission powerof the mobile station, a location code indicating a location of theradio zone (service area), and the like. However, the information itemsother than the wait enabled level and the wait disabled level does nothave to do with the present invention, and the description thereof isomitted.

The control unit 77 ₁ of the mobile station 65 ₁ maintains a controlchannel table listing all the radio channels over which the announcementinformation described above is transmitted from the radio base stationsforming the respective radio zones to which the mobile station 65 ₁ maybe located. Further, upon power-on, the control unit 77 ₁ measuressequentially the electric field intensity L₁ of the control channelregistered in the control table channel by controlling the transmissionand reception unit 74 ₁ ((1) of FIG. 3). A determination is then made asto whether or not the measured electric field intensity is greater thana predetermined threshold level L_(th) ((2) of FIG. 3).

The control unit 77 ₁ registers the control channels for which adetermination that the measured electric field intensity is greater thanthe threshold level L_(th) is obtained, in a prescribed area(hereinafter, referred to as a candidate zone register) in a mainmemory. The electric field intensity of the registered control channelis also registered in the candidate zone register so that thecorrespondence between the control channel and the associated electricfield intensity is specified ((3) of FIG. 3).

When the control unit 77 ₁ has completed a series of the above-describedprocesses (hereinafter, referred to as a measurement process) for allthe control channels registered in the control channel table, thecontrol unit 77 ₁ determines whether or not the candidate zone registerstores any control channel ((4) of FIG. 3). If an affirmative answer isgiven, the control unit 77 ₁ sorts the entries in the candidate zoneregister according to the ascending order of the electric fieldintensity ((5) of FIG. 3).

The control unit 77 ₁ refers to the candidate zone register when thesorting process has been completed and receives the announcementinformation via the individual control channels registered in thecandidate zone register ((6) of FIG. 3). The control unit 77 ₁ measuresthe electric field intensity again ((7) of FIG. 3). Further, the controlunit 77 ₁ compares the electric field intensity L₂ and the wait enabledlevel L_(th) included in the announcement information ((8) of FIG. 3).When the former is lower in level than the latter, a similar comparisonis conducted for the other control channels registered in the candidatezone register ((9) of FIG. 3). Hereinafter, a series of processesperformed subsequent to the measurement process is referred to as a zonedetermination process. The control unit 77 ₁ restarts the measurementprocess when the electric field intensity is found to be below the waitenabled level L_(th) for all the control channels subjected to thecomparison ((10) of FIG. 3).

If the electric intensity field of any of the control channels is foundto be equal to or exceeds the wait enabled level, the control unit 77 ₁establishes that control channel as a control channel for the radio zonein which the mobile station is to register its location, issues a calland receives an incoming call ((11) of FIG. 3). Thereafter, the controlunit 77 ₁ enter a wait state ((12) of FIG. 3).

The operations relating to registering of a location, issuing of a callor receiving of an incoming call performed by the mobile station 65 ₁and the radio base station 61 ₁ are not directly related to the presentinvention, and the description thereof will be omitted below.

The operation performed by the radio base stations 61 ₂-61 ₄ is the sameas the above-described operation of the radio base station 61 ₁, and thedescription thereof is omitted. Also, the operation performed by themobile stations 65 ₂-65 _(N) is the same as the above-describedoperation of the mobile station 65 ₁, and the description thereof isomitted.

In the conventional system described above, if the mobile station 65 ₁is located inside the microcell 63 and near the border with respect tothe radio zone 62 ₁, as indicated by the broken line in FIG. 4, and ifthe electric field intensity of the radio wave arriving from the radiobase station 61 ₁ is higher than that of the radio wave received fromthe radio base station 61 ₃, the mobile station 65 ₁ is set up for await in the radio zone 62 ₁. As illustrated, the radio zone 62 ₁ isformed outside the microcell 63 in which the mobile station 65 ₁ isactually located.

In such a case, the microcell 63 and the picocell 64 provided with theaim of handling a large volume of traffic are not accessed by the mobilestation 65 ₁. The traffic otherwise handled by the microcell 63 isimposed as a load on the radio base station 61 ₁, thus causing theoperating efficiency and the service quality to be dropped.

When the propagation loss of the radio wave that arrives at the mobilestation 65 ₁ from the radio base station 61 ₁ increases due to thepropagation characteristic of the radio transmission channel varyingdepending on the speed of the mobile station mobile station 65 ₁ and thepath of the movement, the mobile station 65 ₁ may leave a zone when itis not necessary and performs the measurement process. Even when a calloriginated in the mobile station 65 ₁ becomes a successful call so thata conversation is established without the mobile station 65 ₁ leavingthe zone, the speech quality may be dropped if there is a largepropagation loss, with the result that switching of message channelsoccur too frequently during the conversation.

Given that the microcell 63 or the picocell 64 is provided in order toserve the dead area located inside the radio zone 62 ₁, the mobilestation 65 ₁ may be set up for a wait in a radio zone located outsidethe cell (the microcell 63 or the picocell 64) in which the mobilestation 65 ₁ is actually located. In this case, the microcell 63 or thepicocell 64 remain unused so that the dead area is not efficientlyserved, a first aspect of the problem with the conventional mobilecommunication system.

A description will now be given, with reference to FIG. 5, of the flowof call origination operation in the conventional mobile communicationsystem, in order to explain a second aspect of the problem with theconventional mobile communication system. In the following explanationof the second aspect, the PDC mobile communication system employedprimarily in Japan is assumed.

In the conventional mobile communication system, when the user of amobile station turns the power on (ST701), the mobile station measures areception level of a perch channel provided for a base station (ST702).A perch channel is a term used in the PDC mobile communication system torefer to a channel provided for each of the base stations to allow amobile station to determine a reception level with respect to the basestation. In the PDC system, a perch channel is mainly used to transmitannouncement information from the base station to the mobile station.The claims refer to a perch channel as a reception-level determiningchannel. If it is determined that the reception level exceeds apredetermined level (YES in ST703), the mobile station sorts the perchchannels according to the ascending order of reception levels and storesthe perch channels and the associated reception levels in a memoryprovided in the mobile station (ST704). A determination is then made asto whether the reception levels in all the perch channels have beenmeasured (ST705).

If no perch channels and associated reception levels are stored in thememory (NO in S706), the mobile station displays an out-of-the-zonemessage in a display device (S707). When perch channels and associatedreception levels are stored in the memory (YES in S706), the mobilestation measures the reception level in the perch channel having thehighest reception level according to the memory. If it is determinedthat the measured reception level exceeds a wait enabled level containedin the announcement information from the base station, the mobilestations is set up for a wait in the base station providing the highestreception level (S708).

The mobile station in a wait state sends a call request to the basestation in which it is set up for a wait (S709). The mobile stationnotifies the base station of the perch channel codes and the receptionlevels provided by the base stations other than the notified basestation.

If the level of reception from the mobile station issuing the requestexceeds a predetermined level that enables assigning of a messagechannel (YES in S710), and if there is an unused message channel (YES inS711), the base station receiving the request from the mobile stationassigns a message channel to the requesting mobile station (S712). Ifthe level of reception from the mobile station is below thepredetermined level (NO in S710), or if there is no unused messagechannel (NO in S711), the base station receiving the request refers tothe reception levels of the adjacent base stations reported by themobile station and designates one of the adjacent base stations as abase station for the requesting mobile station (S713).

The mobile station that receives, from the base station, a signal forassigning a message channel can use the assigned message channel toestablish a call connection with the corresponding base station (S714).

Thus, the mobile station located at a point where there is an overlap ofa plurality of zones formed by respective base stations is set up for await in the base station whose perch channel provides the highestreception level. When originating or receiving a call, the mobilestation issues a request for a message channel to the base station inwhich the mobile station is set up for a wait.

However, it is not always best for the mobile station in the mobilecommunication system to issue a request for a message channel to thebase station providing the highest reception level in the perch channel.

A relatively large service area formed, for example, by the base stationA as shown in FIG. 31 is assumed. This large-zone construction formed bythe base station A may include an area characterized by a concentratedtraffic, resulting in a shortage of message channels in that area. Inorder to remedy this shortage, the base station B having a smallertransmission power and capable of forming a smaller-zone constructionthan the base station A is provided within the service area formed bythe base station A. Provision of the base station B would serve theintended purpose if a mobile station within the zone formed by the basestation B requests a message channel from the base station B.

However, a problem with the conventional mobile communication system isthat the mobile station requests a message channel from the base stationA providing a higher reception level than the base station B instead ofrequesting it from the base station B provided to handle an increasedlocal traffic, with the result that the base station B remains unused tohandle call originating or call incoming in the mobile station.

SUMMARY OF THE INVENTION

Accordingly, a general object of the present invention is to provide amobile communication system and a mobile station apparatus in which theaforementioned problems of the conventional system are eliminated.

Another and more specific object of the present invention is to providea mobile communication system and a mobile station apparatus in which aradio base station adapts itself to a dynamically established trafficdistribution, or in which a mobile station can most successfully enter aradio zone in which it is actually located so as to be set up for a waittherein.

Still another object of the present invention is to assign order ofpriority to a plurality of base stations constituting a mobilecommunication system so that a mobile station requests a message channelfrom a base station having a higher priority than others in order tostart communicating via that base station.

FIG. 6 is a block diagram of a mobile communication system according toclaim 1 of the present invention. The mobile communication systemaccording to claim 1 comprises a plurality of radio base stations 1 ₁-1_(N) forming respective radio zones and effecting a radio channelsetting control in accordance with a predetermined procedure, and amobile station 2 selecting, as a wait zone, one of the radio zones thatsatisfies a criteria demanded by the predetermined procedure, andreceiving communication service via the selected wait zone. Each of theradio base stations 1 ₁-1 _(N) comprises a traffic control unit 3 forsetting a traffic distribution for the plurality of radio zones, and anannouncing unit 4 for generating announcement information including theorder of priority assigned to the plurality of radio zones, the order ofpriority being assigned in accordance with a probability density givento each of the plurality of radio zones under the distribution set bythe traffic control unit 3, and for transmitting the announcementinformation to the radio zone formed by the radio station to which theannouncing unit 4 belongs. The mobile station 2 comprises anannouncement information receiving unit 5 for receiving the announcementinformation transmitted by the announcing unit 4 in accordance with thepredetermined procedure, and a wait control unit 6 for selecting one ofthe radio zones as a wait zone, the radio zone to which a highestpriority is assigned being a first candidate for selection by the waitcontrol unit 6.

FIG. 7 shows a mobile communication system according to claim 2 of thepresent invention. The mobile communication system according to claim 2comprises: a plurality of radio base stations 11 ₁-11 _(N) forming oneor a plurality of radio zones and one or a plurality of small-scaleradio zones, resulting in a hierarchy of overlapping radio zones, andeffecting a radio channel setting control in accordance with apredetermined procedure; and a mobile station 12 accessing one of theradio zones formed by the respective one of the plurality of radio basestations 11 ₁-11 _(N), in accordance with a predetermined procedure, andreceiving communication service via the accessed radio zone. Each of theplurality of radio base stations 11 ₁-11 _(N) comprises an announcingunit 13 for transmitting announcement information which includesidentification information for identifying radio channels assigned torespective radio zones and small-scale radio zones, via the radiochannel assigned to the radio zone formed by the radio base station towhich the announcing unit 13 belongs, the identification informationbeing arranged in the announcement information so as to correspond tothe hierarchy of overlapping radio zones. The mobile station 12comprises: an announcement information receiving unit 14a for receivingthe announcement information transmitted by the announcing unit 13a, inaccordance with the procedure for radio channel setting control; ameasuring unit 15a for measuring an electric field intensity for theradio channel corresponding to the identification information includedin the announcement information received by the announcement informationreceiving unit 14a; and a wait control unit 16a for comparing anelectric field intensity measured by the measuring unit 15a with apreset threshold level, and designating a radio zone to which the radiochannel lowest in the hierarchy is assigned as a wait zone in which toreceive the communication service, on the condition that the electricfield intensity measured by the measuring unit 15a exceeds the presetthreshold level.

The mobile communication system according to claim 3 comprises: aplurality of radio base stations 11 ₁-11 _(N) forming one or a pluralityof radio zones and one or a plurality of small-scale radio zones,resulting in a hierarchy of overlapping zones, and effecting a radiochannel setting control in accordance with a predetermined procedure;and a mobile station 12 accessing one of the radio zones formed by therespective one of the plurality of radio base stations 11 ₁-11 _(N) inaccordance with a predetermined procedure, and receiving communicationservice via the accessed radio zone. Each of the plurality of radio basestations 11 ₁-11 _(N) comprises an announcing unit 13a for transmittingannouncement information which includes identification information foridentifying the one or the plurality of radio zones and the one or theplurality of small-scale radio zones, via the radio channel assigned tothe radio zone formed by the radio base station to which the announcingunit 13a belongs, the identification information being arranged in theannouncement information according to respective positions in thehierarchy of overlapping zones. The mobile station 12 comprises: anannouncement information receiving unit 14a for receiving theannouncement information transmitted by the announcing unit 13a, inaccordance with the procedure for radio channel setting control; ameasuring unit 15a for measuring an electric field intensity for theradio zone corresponding to the identification information included inthe announcement information received by the announcement informationreceiving unit 14a; and a wait control unit 16a for comparing anelectric field intensity measured by the measuring unit 15a with apreset threshold level, and designating, as a wait zone in which toreceive the communication service, a radio zone lowest in the hierarchyof overlapping zones on the condition that the electric field intensitymeasured by the measuring unit 15a exceeds the threshold level.

The mobile communication system according to claim 4 comprises: aplurality of radio base stations 11 ₁-11 _(N) forming one or a pluralityof radio zones and one or a plurality of small-scale radio zones,resulting in a hierarchy of overlapping zones, and effecting a radiochannel setting control in accordance with a predetermined procedure;and a mobile station 12 accessing one of the radio zones formed by therespective one of the plurality of radio base stations 11 ₁-11 _(N) inaccordance with a predetermined procedure, and receiving communicationservice via the accessed radio zone. Each of the plurality of radio basestations 11 ₁-11 _(N) comprises an announcing unit 13b for transmittingannouncement information which includes identification information foridentifying radio channels for the one or the plurality of radio zonesand the one or the plurality of small-scale radio zones, via the radiochannel assigned to the radio zone formed by the radio base station towhich the announcing unit 13b belongs, the identification informationbeing arranged in the announcement information according to respectivepositions in the hierarchy of overlapping zones. The mobile station 12comprises: an announcement information receiving unit 14b for receivingthe announcement information transmitted by the announcing unit 13b, inaccordance with the procedure for radio channel setting control; ameasuring unit 15b for measuring an electric field intensity for theradio channel corresponding to the identification information includedin the announcement information received by the announcement informationreceiving unit 14b; and a wait control unit 16b for comparing anelectric field intensity measured by the measuring unit 15b with apreset threshold level, and designating one of the radio channels, whichis assigned to the radio zone lowest in the hierarchy and for which thecontrol unit 16b has determined that the electric field intensitymeasured by the measuring unit 15b exceeds the preset threshold level,as a radio channel via which to receive the communication service.

The mobile communication system according to claim 5 comprises: aplurality of radio base stations 11 ₁-11 _(N) forming one or a pluralityof radio zones and one or a plurality of small-scale radio zones,resulting in a hierarchy of overlapping zones, and effecting a radiochannel setting control in accordance with a predetermined procedure;and a mobile station 12 accessing one of the radio zones formed by therespective one of the plurality of radio base stations 11 ₁-11 _(N), inaccordance with a predetermined procedure, and receiving communicationservice via the accessed radio zone. Each of the plurality of radio basestations 11 ₁-11 _(N) comprises an announcing unit 13c for transmittingannouncement information which includes identification information foridentifying the one or the plurality of radio zones and the one or theplurality of small-scale radio zones, via the radio channel assigned tothe radio zone formed by the radio base station to which the announcingunit 13c belongs, the identification information being arranged in theannouncement information according to respective positions in thehierarchy of overlapping zones. The mobile station 12 comprises: anannouncement information receiving unit 14c for receiving theannouncement information transmitted by the announcing unit 13c, inaccordance with the procedure for radio channel setting control; ameasuring unit 15c for measuring an electric field intensity for theradio zone corresponding to the identification information included inthe announcement information received by the announcement informationreceiving unit 14c; and a wait control unit 16c for comparing anelectric field intensity measured by the measuring unit 15c with apreset threshold level, and designating, as a wait zone in which toreceive the communication service, a radio zone identified by theidentification information to be lowest in the hierarchy of overlappingzones, on the condition that the electric field intensity measured bythe measuring unit 15a exceeds the threshold level.

The mobile communication system according to claim 6 comprises: aplurality of radio base stations 11 ₁-11 _(N) forming one or a pluralityof radio zones and one or a plurality of small-scale radio zones,resulting in a hierarchy of overlapping zones, and effecting a radiochannel setting control in accordance with a predetermined procedure;and a mobile station 12 accessing one of the radio zones formed by therespective one of the plurality of radio base stations 11 ₁-11 _(N), inaccordance with a predetermined procedure, and receiving communicationservice via the accessed radio zone. Each of the plurality of radio basestations 11 ₁-11 _(N) comprises an announcing unit 13d for transmittingannouncement information which includes first identification informationfor identifying a radio channel assigned to the radio zone formed by theradio base station to which the announcing unit 13d belongs, as well asincluding second identification information identifying the radio zonesand the small-scale radio zones which overlap the radio zone formed bythe radio base station to which the announcing unit 13d belongs, via theradio channel assigned to the radio zone formed by the radio basestation to which the announcing unit 13d belongs, the secondidentification information being arranged in the announcementinformation according to respective positions in the hierarchy ofoverlapping zones. The mobile station 12 comprises: an announcementinformation receiving unit 14d for receiving the announcementinformation transmitted by the announcing unit 13d, in accordance withthe procedure for radio channel setting control; a measuring unit 15dfor measuring an electric field intensity for the radio channelcorresponding to the identification information included in theannouncement information received by the announcement informationreceiving unit 14d; and a wait control unit 16d for comparing anelectric field intensity measured by the measuring unit 15d with apreset threshold level, determining the radio channel which isidentified by the associated second identification information, ifavailable, to have a lowest hierarchical order, and designating, as await zone in which to receive the communication service, the radio zoneto which the determined radio channel is assigned, on the condition thatthe electric field intensity measured by the measuring unit 15d exceedsthe threshold level.

The mobile communication system according to claim 7 comprises: aplurality of radio base stations 11 ₁-11 _(N) forming one or a pluralityof radio zones and one or a plurality of small-scale radio zones,resulting in a hierarchy of overlapping zones, and effecting a radiochannel setting control in accordance with a predetermined procedure;and a mobile station 12 accessing one of the radio zones formed by therespective one of the plurality of radio base stations 11 ₁-11 _(N) inaccordance with a predetermined procedure, and receiving communicationservice via the accessed radio zone. Each of the plurality of radio basestations 11 ₁-11 _(N) comprises an announcing unit 13e for transmittingannouncement information which includes first identification informationfor identifying a radio channel assigned to a radio zone formed by theradio base station to which the announcing unit 13e belongs, as well asincluding second identification information identifying the radio zonesand the small-scale radio zones which overlap the radio zone formed bythe radio base station to which the announcing unit 13e belongs, overthe radio zone formed by the radio base station to which the announcingunit 13e belongs, the second identification information being arrangedin the announcement information according to respective positions in thehierarchy of overlapping zones. The mobile station 12 comprises: anannouncement information receiving unit 14e for receiving theannouncement information transmitted by the announcing nit 13e, inaccordance with the procedure for radio channel setting control; ameasuring unit 15e for measuring an electric field intensity for theradio zone corresponding to the identification information included inthe announcement information received by the announcement informationreceiving unit 14e; and a wait control unit 16e for comparing anelectric field intensity measured by the measuring unit 15e with apreset threshold level, determining the radio zone corresponding to theradio channel which is identified by the associated secondidentification information, if available, to have a lowest hierarchicalorder, and designating the determined radio zone as a wait zone in whichto receive the communication service on the condition that the electricfield intensity measured by the measuring unit 15e exceeds the thresholdlevel.

The mobile communication system according to claim 8 comprises: aplurality of radio base stations 11 ₁-11 _(N) forming one or a pluralityof radio zones and one or a plurality of small-scale radio zones,resulting in a hierarchy of overlapping zones, and effecting a radiochannel setting control in accordance with a predetermined procedure;and a mobile station 12 accessing one of the radio zones formed by therespective one of the plurality of radio base stations 11 ₁-11 _(N), inaccordance with a predetermined procedure, and receiving communicationservice via the accessed radio zone. Each of the plurality of radio basestations 11 ₁-11 _(N) comprises an announcing unit 13f for transmittingannouncement information which includes a hierarchical (equal orsubordinate) order of the radio zone formed by the radio base station towhich the announcing unit 13f belongs with respect to the overlappingradio zones and small-scale radio zones, and which also includesidentification information for identifying radio channels assigned tothe radio zone formed by the radio base station to which the announcingunit 13f belongs and the overlapping radio zones and small-scale radiozones, via the radio channel assigned to the radio zone formed by theradio base station to which the announcing unit 13f belongs. The mobilestation 12 comprises: an announcement information receiving unit 14f forreceiving the announcement information transmitted by the announcingunit 13f, in accordance with the procedure for radio channel settingcontrol, for extracting the identification information from theannouncement information, and for determining the hierarchy of the radiozones to which the radio channels identified by the identificationinformation are assigned; a measuring unit 15f for measuring an electricfield intensity for the radio channel corresponding to theidentification information obtained by the announcement informationreceiving unit 14f, and a wait control unit 16f for comparing anelectric field intensity measured by the measuring unit 15f with apreset threshold level, and designating a radio zone to which the radiochannel lowest in the hierarchy is assigned as a wait zone in which toreceive the communication service, on the condition that the electricfield intensity measured by the measuring unit 15f for the radio channellowest in the hierarchy exceeds the preset threshold level.

The mobile communication system according to claim 9 comprises: aplurality of radio base stations 11 ₁-11 _(N) forming one or a pluralityof radio zones and one or a plurality of small-scale radio zones,resulting in a hierarchy of overlapping zones, and effecting a radiochannel setting control in accordance with a predetermined procedure;and a mobile station 12 accessing one of the radio zones formed by therespective one of the plurality of radio base stations 11 ₁-11 _(N), inaccordance with a predetermined procedure, and receiving communicationservice via the accessed radio zone. Each of the plurality of radio basestations 11 ₁-11 _(N) comprises an announcing unit 13g for transmittingannouncement information which includes a hierarchical (equal orsubordinate) order of the radio zone formed by the radio base station towhich the announcing unit 13g belongs with respect to the overlappingradio zones and small-scale radio zones, and which also includesidentification information for identifying the radio zone formed by theradio base station to which the announcing unit 13g belongs and theoverlapping radio zones and small-scale radio zones, over the radio zoneformed by the radio base station to which the announcing unit 13gbelongs. The mobile station 12 comprises: an announcement informationreceiving unit 14g for receiving the announcement informationtransmitted by the announcing unit 13g, in accordance with the procedurefor radio channel setting control, for extracting the identificationinformation from the announcement information, and for determining thehierarchy of the radio zones corresponding to the identificationinformation; a measuring unit 15g for measuring an electric fieldintensity for the radio zone corresponding to the identificationinformation extracted by the announcement information receiving unit14g; and a wait control unit 16g for comparing an electric fieldintensity measured by the measuring unit 15g with a preset thresholdlevel, and designating a radio zone lowest in the hierarchy determinedby the announcement information receiving unit 14g as a wait zone inwhich to receive the communication service, on the condition that theelectric field intensity measured by the measuring unit 15g for theradio zone lowest in the hierarchy exceeds the preset threshold level.

The announcing unit of the mobile communication system according toclaim 10 comprises a unit for adding, in the announcement information,preset threshold values individually provided for the radio zone formedby the radio base station to which the announcing unit belongs and theoverlapping radio zones and small-scale radio zones, resulting in ahierarchy that corresponds to the hierarchy of overlapping zones. Thewait control unit 16 employs the threshold values added to theannouncement information by the announcing unit in making comparisonswith the electric field intensity.

The announcing unit of the mobile communication system according toclaim 11 comprises a unit for adding a relative value indicating thepreset threshold value for the zone formed by the radio base station towhich the announcing unit belongs, in the form of a difference withrespect to a reference value for the threshold value. The announcementinformation receiving unit includes a unit for determining the relativevalue added to the announcement information, in relation to the radiozone in which the announcement information is received. The wait controlunit compares the electric field intensity measured by the measuringunit with a sum of the reference value and the relative value determinedby the announcement information receiving unit in relation to the radiozone in which the electric field intensity is measured.

The announcing unit of the mobile communication system according toclaim 12 comprises a unit for adding relative values indicating thepreset threshold values for the radio zone formed by the radio basestation to which the announcing unit belongs and the overlapping radiozones and small-scale radio zones, in the form of differences withrespect to a reference value common to the threshold values, resultingin a hierarchy that corresponds to the hierarchy of overlapping zones.The wait control unit compares the electric field intensity with a sumof the relative value and the reference value.

The mobile station 12 of the mobile communication system according toclaim 13 comprises a zone determination unit 17 for performing a cyclicmeasurement of the electric field intensity of the radio zones in whichthe mobile station 12 can be located, comparing a measured electricfield intensity with a lower acceptance value by which an entry into theradio zone is enabled, stopping processes of measurement and comparisonwhen it is found that the former exceeds the latter, and selecting theassociated radio zone as a candidate in which the announcementinformation receiving unit 14 is to receive the announcementinformation.

The wait control unit of the mobile communication system according toclaim 14 compares the electric field intensity measured by the measuringunit with the threshold value in the descending order of the hierarchyin the radio zones subject to the measurement, and designates the radiozone for which it is found that the former exceeds the latter as a waitzone.

The measuring unit of the mobile communication system according to claim15 comprises a unit which omits a measurement of the radio zone selectedby the zone determination unit 17 and substitutes therefor the electricfield intensity measured by the zone determination unit.

FIG. 8 is a block diagram showing the invention described in claim 16.

The mobile station according to claim 16 comprises an announcementinformation receiving unit 21 for receiving announcement informationincluding orders of priority assigned to radio zones formed by aplurality of radio base stations, the reception by the announcementinformation receiving unit 21 being conducted according to a descendingorder of preset traffic distribution and in accordance with a radiochannel setting control procedure; a wait unit 23 for determiningwhether the radio zone associated with the order of priority included inthe announcement information received by the announcement informationreceiving unit 21 satisfies a criteria adapted for the radio channelsetting control procedure, and for designating the radio zone for whichan affirmative answer is given as a wait zone; and a communicationcontrol unit 25 which receives communication service from the radio basestation forming the radio zone designated by the wait unit 23.

The mobile communication system according to claim 17 comprises: aplurality of base stations forming respective radio zones that overlapeach other; a mobile station transportable between said radio zones;wherein each of said plurality of base stations comprises: announcingmeans for sending announcement information including an order ofpriority of said plurality of base stations to the mobile stationlocated in one of said radio zones, and said mobile station comprises:control means for selecting the base station to which a request for amessage channel is to be issued, based on the order of priority of thebase stations included in the announcement information transmitted fromsaid plurality of base stations.

According to this aspect of the present invention, the base station asshown in FIG. 31 in which the mobile station is set up for a waittransmits the announcement information that includes the order ofpriority specifying, for example, that the base station B be given thepriority over the base station A in selecting a base station from whichto request a message channel. Therefore, the mobile station requests amessage channel from the base station B in accordance with the order ofpriority included in the announcement information from the base stationA.

Since the mobile station requests a message channel from the basestation B instead of the base station A providing a higher receptionlevel, the base station B can be used efficiently to handle calloriginating and call incoming in the mobile station.

The mobile station according to claim 18 further comprises: announcementinformation receiving means for receiving the announcement informationincluding the order of priority of said plurality of base stations andtransmitted from said plurality of base stations; and transmission meansfor issuing a request for a message channel to the base station selectedby said control means.

According to this aspect of the present invention, the announcementinformation receiving means of the mobile station receives theannouncement information including the order of priority of the basestations from, for example, the base station A and the base station B asshown in FIG. 31. The transmission means of the mobile station transmitsa request for a message channel from a base station selected by thecontrol means. For example, the mobile station may send the request tothe base station B having the highest priority.

The mobile station according to claim 19 further comprises: storagemeans for storing the announcement information; measuring means formeasuring a reception level in reception-level determining channels in adescending order of priority of said plurality of base stations, basedon the announcement information stored in said storage means andincluding the order of priority and based on information relating to thereception-level determining channels.

According to this aspect of the present invention, the memory means ofthe mobile station stores the announcement information received by theannouncement information receiving means from, for example, the basestation A and the base station B as shown in FIG. 31 and including theorder of priority of the base stations. Measurement of the receptionlevel by the measuring means starts with the base station B having thehighest priority, based on the order of priority of the base stations Aand B stored in the storing means and the information relating to theperch channel corresponding to the respective base stations. Themeasuring means notifies the control means of the reception level.

Therefore, the mobile station stores the order of priority of the basestations included in the announcement information received by theannouncement information receiving means and notifies the control meansof the reception level so that selection can be made on the base stationto which a request for a message channel is to be issued. In this way,the control means is able to select the base station B to which therequest should be sent.

The control means according to claim 20 includes determining means fordetermining whether the reception level in a reception-level determiningchannel is equal to or exceeds a predetermined level that enables arequest for a message channel.

According to this aspect of the present invention, the control means ofthe mobile station can determine whether the reception level of theperch channel of, for example, the base station A or the base station Bas shown in FIG. 31 is equal to or exceeds a predetermined level.

The announcing means according to claim 21 includes first arrangingmeans for ordering the announcement information so as to arrangeinformation relating to reception-level determining channels in adescending order of priority.

According to this aspect of the present invention, the announcing meansof, for example, the base station A as shown FIG. 31 can order theannouncement information such that information relating to the perchchannel of the base station A and that of the base station B arearranged in the order of priority.

The announcing means according to claim 22 includes second arrangingmeans for ordering the announcement information so as to coupleinformation relating to each reception-level determining channel to anorder of priority associated therewith.

According to this aspect of the present invention, the announcing meansof, for example, the base station A as shown in FIG. 31 can order theannouncement information such that information relating to the perchchannel of the base station A is coupled to the priority assignedthereto and information relating to the perch channel of the basestation B is coupled to the priority assigned thereto.

The transmission means according to claim 23 includes first transmissionmeans for issuing a request for a message channel to the base stationselected by the control means when a call is originated.

According to this aspect of the present invention, the control means ofthe mobile station as shown in FIG. 31 can select the base station Bassigned the highest priority when the mobile station originates a call,so that the transmission means can request a message channel from thebase station B.

The transmission means according to claim 24 includes secondtransmission means for issuing a request for a message channel to thebase station selected by the control means when a call is incoming.

According to this aspect of the present invention, the control means ofthe mobile station as shown in FIG. 31 can select the base station Bassigned the highest priority when the mobile station receives anincoming call, so that the transmission means can request a messagechannel from the base station B.

The transmission means according to claim 25 includes third transmissionmeans for transmitting a request for a communication to the base stationselected by the control means when a message channel is switched fromone to another in the event of a handover of a call.

According to this aspect of the present invention, the control means ofthe mobile station as shown in FIG. 31 can select the base station Bassigned the highest priority when a switching of channels occurs in theevent of a handover, so that the transmission means can request amessage channel from the base station B.

The mobile station according to claim 26 comprises control means forselecting a base station to which a request for a message channel is tobe issued, based on an order of priority of a plurality of base stationsincluded in announcement information from said plurality of basestations.

Referring to 31, based on the announcement information from the basestation A including the order of priority of the base stations A and B,the mobile station can request a message channel from the base station Binstead of the base station A providing a higher reception level. Thus,the base station B, provided to handle an increased local traffic, canbe efficiently used to handle call originating and call incoming in themobile station.

The mobile station according to claim 27 comprises: announcementinformation receiving means for receiving, from said plurality of basestations, the announcement information including the order of priorityof said plurality of base stations; and transmission means fortransmitting a request for a message channel to the base stationselected by said control means.

According to this aspect of the present invention, the announcementinformation receiving means of the mobile station receives theannouncement information including the order of priority of the basestations from, for example, the base station A and the base station B asshown in FIG. 31. The transmission means of the mobile station transmitsa request for a message channel from a base station selected by thecontrol means. For example, the mobile station may send the request tothe base station B having the highest priority.

The mobile station according to claim 28 comprises: storage means forstoring the announcement information; measuring means for measuring areception level in reception-level determining channels in a descendingorder of priority of said plurality of base stations, based on theannouncement information stored in said storage means and including theorder of priority and based on information relating to thereception-level determining channels.

According to this aspect of the present invention, the memory means ofthe mobile station stores the announcement information received by theannouncement information receiving means from, for example, the basestation A and the base station B as shown in FIG. 31 and including theorder of priority of the base stations. Measurement of the receptionlevel by the measuring means starts with the base station B having thehighest priority, based on the order of priority of the base stations Aand B stored in the storing means and the information relating to theperch channel corresponding to the respective base stations. Themeasuring means notifies the control means of the reception level.

Therefore, the mobile station stores the order of priority of the basestations included in the announcement information received by theannouncement information receiving means and notifies the control meansof the reception level so that selection can be made on the base stationto which a request for a message channel is to be issued. In this way,the control means is able to select the base station B to which therequest should be sent.

The control means according to claim 29 includes determining means fordetermining whether the reception level in a reception-level determiningchannel is equal to or exceeds a predetermined level that enables arequest for a message channel.

According to this aspect of the present invention, the control means ofthe mobile station can determine whether the reception level of theperch channel of, for example, the base station A or the base station Bas shown in FIG. 31 is equal to or exceeds a predetermined level.

The transmission means according to claim 30 includes first transmissionmeans for issuing a request for a message channel to the base stationselected by the control means when a call is originated.

According to this aspect of the present invention, the control means ofthe mobile station as shown in FIG. 31 can select the base station Bassigned the highest priority when the mobile station originates a call,so that the transmission means can request a message channel from thebase station B.

The transmission means according to claim 31 includes secondtransmission means for issuing a request for a message channel to thebase station selected by the control means when a call is incoming.

According to this aspect of the present invention, the control means ofthe mobile station as shown in FIG. 31 can select the base station Bassigned the highest priority when the mobile station receives anincoming call, so that the transmission means can request a messagechannel from the base station B.

The transmission means according to claim 32 includes third transmissionmeans for transmitting a request for a communication to the base stationselected by the control means when a message channel is switched fromone to another in the event of a handover of a call.

According to this aspect of the present invention, the control means ofthe mobile station as shown in FIG. 31 can select the base station Bassigned the highest priority when a switching of channels occurs in theevent of a handover, so that the transmission means can request amessage channel from the base station B.

The base station according to claim 33 comprises: announcing means forsending announcement information including an order of priority of aplurality of base stations constituting the mobile communication systemto a mobile station located in one of the radio zones.

A mobile communication system as shown in FIG. 31 is assumed. The basestation A forms a relatively large service area (zone) and a basestation B having a smaller transmission power than the base station Aforms a relatively small service area (zone) inside the service areaformed by the base station A. The mobile station is set up for a wait inthe base station A. According to the invention of claim 33, the basestation A can transmit the announcement information including the orderof priority of the base stations. For example, the base station B couldbe given a higher priority over the base station A according to theannouncement information.

The announcing means according to claim 34 includes first arrangingmeans for ordering the announcement information so as to arrangeinformation relating to reception-level determining channels in adescending order of priority.

According to this aspect of the present invention, the announcing meansof, for example, the base station A as shown FIG. 31 can order theannouncement information such that information relating to the perchchannel of the base station A and that of the base station B arearranged in the order of priority.

The announcing means according to claim 35 includes second arrangingmeans for ordering the announcement information so as to coupleinformation relating to each reception-level determining channel to anorder of priority associated therewith.

According to this aspect of the present invention, the announcing meansof, for example, the base station A as shown in FIG. 31 can order theannouncement information such that information relating to the perchchannel of the base station A is coupled to the priority assignedthereto and information relating to the perch channel of the basestation B is coupled to the priority assigned thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and further features of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings, in which:

FIG. 1 shows a construction of a conventional mobile communicationsystem;

FIG. 2 shows a construction of conventional announcement information;

FIG. 3 is a flowchart of a conventional operation;

FIG. 4 illustrates a problem with the conventional mobile communicationsystem;

FIG. 5 is a flowchart showing the conventional call originationoperation;

FIG. 6 is a block diagram of a mobile communication system according tothe invention described in claim 1;

FIG. 7 is a block diagram showing a principle of the invention describedin claims 2-15;

FIG. 8 is a block diagram showing a principle of the invention describedin claim 16;

FIG. 9 is a flowchart of an operation of a system according to theinvention described in claims 2, 3, 14-16;

FIG. 10 shows a format of announcement information according to anembodiment that corresponds to the invention described in claims 2 and3;

FIG. 11 is a flowchart of an operation according to an embodiment thatcorresponds to the invention described in claims 4-9, 14 and 15;

FIG. 12 shows a format of announcement information according to anembodiment that corresponds to the invention described in claims 4-7;

FIG. 13 shows a format of announcement information according to anembodiment that corresponds to the invention described in claims 8 and9;

FIG. 14 is a flowchart of an operation according to an embodiment thatcorresponds the invention described in claims 10, 14 and 15;

FIG. 15 shows a format of announcement information according to anembodiment that corresponds to the invention described in claim 10;

FIG. 16 is a flowchart of an operation according to an embodiment thatcorresponds to the invention described in claims 11, 12, 14 and 15;

FIG. 17 shows announcement information according to an embodiment thatcorresponds to the invention described in claims 11 and 12;

FIG. 18 is a flowchart of an operation according to an embodiment thatcorresponds to the invention described in claims 13-15;

FIG. 19 shows a mobile communication system directed to resolving theproblem with the conventional message channel assigning operation;

FIG. 20 shows a mobile communication system to which the presentinvention is applied;

FIG. 21A shows how the announcement information is delivered;

FIG. 21B shows the principle of the flow of the call originationoperation according to the present invention;

FIG. 22 shows a format of the announcement information according to thepresent invention;

FIG. 23 shows another format of the announcement information accordingto the present invention;

FIG. 24 shows still another format of the announcement informationaccording to the present invention;

FIG. 25 is a flowchart showing the flow of the call originationoperation according to the present invention;

FIG. 26 shows a sequence of the call origination operation according tothe present invention;

FIG. 27 shows the flow of the call-incoming operation according to thepresent invention;

FIG. 28 shows the sequence of the call-incoming operation according tothe present invention;

FIG. 29 shows the flow of a recall channel switching operation accordingto the present invention;

FIG. 30 shows the sequence of the recall channel switching operationaccording to the present invention;

FIG. 31 shows how base stations are ordered;

FIG. 32 shows a hardware construction of a base station assumed in thepresent invention; and

FIG. 33 shows a hardware construction of a mobile station assumed inpresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The inventive feature of an embodiment that corresponds to the inventiondescribed in claim 1 consists in the constitution of the announcementinformation sent by the base station control devices 69 ₁-69 ₄ of theradio base stations 61 ₁-61 ₄ to the control channel, and in theprocedure of radio channel setting control effected by the control units77 ₁-77 _(N) of the mobile stations 65 ₁-65 _(N), respectively, inaccordance with the announcement information. The hardware configurationof the system according to the embodiment that corresponds to theinvention described in claim 1 is the same as the conventional systemshown in FIG. 1, and the description thereof is omitted.

The radio base stations 61 ₁-61 ₄ correspond to the radio base stations1 ₁-1 _(N) shown in FIG. 6, respectively. Each of the radio basestations 1 ₁-_(N) includes the respective traffic control unit 3 and theannouncing unit 4. The mobile stations 65 ₁-65 _(N) correspond to themobile station 2 which includes the announcement information receivingunit 5 and the wait control unit 6.

A description will now be given, with reference to FIG. 1, of theoperation of the system that corresponds to the invention described inclaim 1.

Each of the base station control devices 69 ₁-69 ₄ of the radio basestations 61 ₁-61 ₄, respectively, maintains a data base (not shown).Such a data base assigns a weight to each of the radio base stations 61₁-61 ₄ so as to arrange the radio base stations 61 ₁-61 ₄ in the orderof priority. The weight is determined by a condition such as theoperating mode and the current traffic. The operating mode could includethe day of the week, the time zone of the day and the like.

Each of the base station control devices 69 ₁-69 ₄ also monitors callsoriginated in mobile stations located in a radio zone formed by therespective base station, so that the traffic in that radio zone can bemeasured. The measured traffic is reported to the other base stationsvia a communication link (not shown).

Further, each of the base station control devices 69 ₁-69 ₄ refers tothe above-mentioned data base against the traffic measured locally, thetraffic reported by the other base stations, and the day of the week andthe time zone, so as to determine a combination of weights suitable forthe combination of the ongoing traffic. Each of the base station controldevices 69 ₁-69 ₄ then incorporates the determined combination in theannouncement information in relation to the respective radio zones 62₁-62 ₄ (or the radio base stations 61 ₁-61 ₄). The announcementinformation is transmitted via the transmission and reception units 68₁-68 ₄, the common antenna equipment units 67 ₁-67 ₄ and the antennas 66₁-66 ₄.

The control unit 77 ₁ of the mobile station 65 ₁ effects a measurementprocess and a zone determination process as in the conventional system.Given that there are a plurality of candidate radio zones which themobile station 65 ₁ may enter, the radio zone to which the greatestweight is assigned in the announcement information is selected as thefirst candidate zone for entry so that the control unit 77 ₁ can enter await state.

Thus, according to the embodiment that corresponds to the inventiondescribed in claim 1, the distribution of the mobile stations set up fora wait in respective radio zones can be varied dynamically so as to beadapted for the operating condition and the operating mode of the radiobase stations. Therefore, maintenance and operating requirements areflexibly met and the resources such as the radio base stations and theradio frequencies are effectively utilized.

In the above-described embodiments, the weights are determined by thetraffic distribution in the radio zones, the day of the week and thetime zone. However, the weight may be appropriately provided incorrespondence with events detected in the process of the monitoringcontrol and the radio channel setting control effected by the radio basestations. Such events may be various failures and releases therefrom, orcongestions in radio channels.

FIG. 8 is a flowchart of an operation of the mobile communication systemaccording to embodiments that correspond to the invention described inclaims 2, 3 and 14-16.

The inventive feature of the embodiments that correspond to theinvention described in claims 2, 3 and 14-16 consists in theconstitution of the announcement information sent by the base stationcontrol devices 69 ₁-69 ₄ of the radio base stations 61 ₁-61 ₄ to thecontrol channel, and in the procedure of radio channel setting controlprocess effected by the control units 77 ₁-77 _(N) of the mobilestations 65 ₁-65 _(N), respectively, in accordance with the announcementinformation. The hardware configuration of the embodiments thatcorrespond to the invention described in claims 2, 3 and 14-16 is thesame as that of the conventional system shown in FIG. 1, and thedescription thereof is omitted.

The radio base stations 61 ₁-61 ₄ correspond to radio base stations 11₁-11 _(N) which include announcing units 13 and 13a-13g, respectively.The mobile stations 65 ₁-65 _(N) correspond to a mobile station 12 whichincludes one of announcing information receiving units 14 and 14a-14g(in the case of claim 2) or an announcing information receiving unit 21(in the case of claim 16). The mobile station 12 also includes one ofmeasuring units 15 and 15a-15g, one of wait control units 16 and16a-16g, an entry determining unit 17, a wait unit 23, and acommunication control unit 25.

A description will now be given of the operation of the system accordingto embodiments that correspond to the invention described in claims 2, 3and 16. For the sake of simplicity of the description that follows, itis assumed that the mobile station 65 ₁ is located in the same locationassumed in the description of the related art.

In the absence of a hierarchy of radio zones (hereinafter, referred toas overlap zones) embodied by a microcell 63, a picocell 64 and the likeat respective locations in a radio zone formed by the radio base station61 ₁, the base station control device 69 ₁ of the radio base station 61₁ transmits the announcement information having the same format as thatof the conventional announcement information as shown in FIG. 2, via thetransmission and reception unit 68 ₁, the common antenna equipment unit67 ₁ and the antenna 66 ₁.

If there are overlap zones, the base station control device 69 ₁ isprovided by a control station (not shown) with an identification code C₁for a control channel formed by the radio base station 61 ₁ andidentification codes C₃ and C₄ for control channels (hereinafter,referred to as overlap control channels) assigned to the microcell 63and the picocell 64 embodying the overlap zones, via the communicationlink 71 ₁ and the transmission device 70 ₁. As indicated by a hatchedarea in FIG. 10, the base station control device 69 ₁ incorporates, inthe announcement information, the identification codes C₁ and C₃-C₄ forthe control channel and the overlap control channels, respectively, suchthat a series of the identification codes C₄, C₃ and C₁ are arrangedaccording to respective positions in the hierarchy. The wait enabledlevel and the wait disabled level are also included in the announcementinformation as in the conventional system.

The control unit 77 ₁ of the mobile station 65 ₁ effects the measurementprocess and the zone determination process as in the conventionalsystem. In the zone determination process, a determination as to whetherthe format of the announcement information received via the controlchannel subject to the measurement of the electric field intensity L₂ isthe same as the conventional format shown in FIG. 2 is made, dependingon whether the above-described series of the identification codes isincluded in the announcement information ((1) of FIG. 9).

If the format of the announcement information is found to be the same asthe conventional format, the control unit 77 ₁ performs the zonedetermination process in accordance with the same procedure as observedin the conventional system before proceeding to a wait state ((2) ofFIG. 9).

If the format of the announcement information is not found to be thesame as the conventional format, the control unit 77 ₁ stores the seriesof the identification codes C₄, C₃ and C₁ in a reserved area(hereinafter, referred to as a selected candidate zone register) in themain memory ((3) of FIG. 9). The control unit 77 ₁ sequentially refersto the identification codes C₄, C₃ and C₁ and measures the electricfield intensity L₃ of the overlap control channels and the controlchannel corresponding to the respective identification codes ((4) ofFIG. 9). The control unit 77 ₁ then compares the measured electric fieldintensity with the wait enabled level L_(th) received in theannouncement information via the channel subject to the measurement ((5)of FIG. 9).

If the electric field L₃ is found to exceed the wait enabled levelL_(th), the control unit 77 ₁ retains the relevant identification codein the selected candidate zone register. If the opposite is the case,the relevant identification code is removed ((6) of FIG. 9).

When the control unit 77 ₁ has processed all the identification codesstored in the candidate zone register, a determination is made as towhether or not the selected candidate zone register contains anyidentification code ((7) of FIG. 9). When the determination in (7) givesa negative answer, the control unit 77 ₁ performs the zone determinationprocess in accordance with the conventional procedure before proceedingto a wait state ((8) of FIG. 9).

When the determination in (7) gives a positive answer, the control unit77 ₁ designates an overlap control channel (or a control channel)specified by the identification code stored earliest in the selectedcandidate zone register as a control channel for a radio zone in whichthe mobile station 65 ₁ is to receive the communication service, andproceeds to be set up for a wait in the designated control channel ((9)of FIG. 9).

Thus, in the system described above, the mobile stations 65 ₁-65 _(N)give a priority to the microcell 63 over the radio zone 62 ₁, and give apriority to the picocell 64 over the microcell 63, in selecting a waitzone. In contrast with the conventional system in which the wait zone isselected simply in accordance with the order of electric field intensityof the associated control channels, the embodiments that correspond tothe invention described in claims 2, 3 and 14-16 ensure that the mobilestation can wait in the most appropriate zone than the conventionalsystem.

In the foregoing description, it is assumed that the mobile stations 65₁-65 _(N) are implemented by the mobile station described in claim 16.However, mobile stations according to different embodiments may also beemployed.

FIG. 11 is a flowchart of an operation of the mobile communicationsystem according to embodiments that correspond to the inventiondescribed in claims 4-9, 14 and 15.

A description will now be given, with reference to FIGS. 1 and 11, ofthe operation of the system according to embodiments that correspond toinvention described in claims 4-7. For the sake of simplicity of thedescription that follows, it is assumed that the mobile station 65 ₁ islocated in the same location assumed in the description of the relatedart.

In the absence of overlap zones such as a microcell 63, a picocell 64and the like at respective locations in a radio zone formed by the radiobase station 61 ₁, the base station control device 69 ₁ of the radiobase station 61 ₁ transmits the announcement information having the sameformat as that of the conventional announcement information as shown inFIG. 2, via the transmission and reception unit 68 ₁, the common antennaequipment unit 67 ₁ and the antenna 66 ₁.

If there are overlap zones, the base station control device 69 ₁ isprovided by a control station (not shown) with an identification code C₁for a control channel assigned to the radio base station 61 ₁,identification codes C₃ and C₄ for overlap control channels assigned tothe microcell 63 and the picocell 64 embodying the overlap zones, andnumerals P₁, P₃ and P₄ indicating the hierarchical order of the radiozone 62 ₁, the microcell 63 and the picocell 64, via the communicationlink 71 ₁ and the transmission device 70 ₁. The numerals will be simplyreferred to as the order of priority. For the sake of simplicity of thedescription, it is assumed that the radio zone 62 ₁ has the order ofpriority P₁=0, the microcell 63 P₃=1 and the picocell 64 P₄=2.

As indicated by a hatched area in FIG. 12, the base station controldevice 69 ₁ incorporates, in the announcement information, theidentification codes C₁ and C₃-C₄, and the orders of priority P₁, P₃ andP₄ such that a resultant series of identification information C₁, P₁,C₃, P₃, C₄ and P₄ show correspondences between the individual channelsand the order of priority associated therewith. The wait enabled leveland the wait disabled level are also included in the announcementinformation as in the conventional system.

The control unit 77 ₁ of the mobile station 65 ₁ effects the measurementprocess and the zone determination process as in the conventionalsystem. In the zone determination process, a determination as to whetherthe format of the announcement information received via the controlchannel subject to the measurement of the electric field intensity L₂ isthe same as the conventional format shown in FIG. 2 is made, dependingon whether the above-described series of the identification informationis included in the announcement information ((1) of FIG. 11).

If the format of the announcement information is found to be the same asthe conventional format, the control unit 77 ₁ performs the zonedetermination process in accordance with the same procedure as observedin the conventional system before proceeding to a wait state ((2) ofFIG. 11).

If the format of the announcement information is not found to be thesame as the conventional format, the control unit 77 ₁ stores the seriesof the identification information C₁, P₁, C₃, P₃, C₄ and P₄ in theselected candidate zone register in the main memory ((3) of FIG. 11).The control unit 77 ₁ sorts the combinations of the identification codesand the orders of priority stored in the selected candidate zoneregister, in the ascending order of priority. Once this sorting is done,all the orders of priority are removed from the register, resulting inthe series of identification information consisted only of theidentification codes being stored in the selected candidate zoneregister ((a) of FIG. 11).

The control unit 77 ₁ sequentially refers to the identification codesC₄, C₃ and C₁ and measures the electric field intensity L₃ of theoverlap control channels and the control channel corresponding to therespective identification codes ((4) of FIG. 11). The control unit 77 ₁then compares the measured electric field intensity with the waitenabled level L_(th) received in the announcement information via thechannel subject to the measurement ((5) of FIG. 11).

When the result of the comparison is available, the control unit 77 ₁then enters a wait state in accordance with the same procedure asobserved in the embodiment that corresponds to the invention describedin claim 2. The steps subsequent to (5) of FIG. 11 are designated by thesame reference numerals (6)-(9) as the corresponding steps of FIG. 9,and the description thereof is omitted.

According to embodiments that correspond to the invention described inclaims 4-9, 14 and 15, as long as the correspondences between theidentification codes and the respective orders of priority areestablished, it is possible for the radio base stations 61 ₁-61 ₄ totransmit identification information as part of the announcementinformation irrespective of the order of priority. Accordingly, aflexible operation of the radio base stations 61 ₁-61 ₄ allowingaddition of radio zones or reforming is enabled. As in the embodimentthat corresponds to the invention described in claims 2 and 3, it ispossible for the mobile stations 65 ₁-65 ₄ to give a priority to themicrocell 63 over the radio zone 62 ₁ and to give a priority to thepicocell 64 over the microcell 63, in selecting a wait zone.

According to the embodiment that corresponds to the invention describedin claims 4-9, 14 and 15, the series of identification information (C₁,P₁, C₃, P₃, C₄, P₄) stored in the selected candidate zone register issorted in the ascending order of the priority, and then theidentification information consisting only of the identification codesare retained in the selected candidate zone register. An alternativeprocedure may be to retain the orders of priority in the selectedcandidate zone register so that the identification code with the highestpriority may be referred to in selecting a wait zone.

As shown in FIG. 12, according to the embodiment that corresponds to theinvention described in claims 4-9, 14 and 15, the radio base station 61₁ transmits, as part of the announcement information, the order ofpriority P₁ for the radio zone 62 ₁ in relation to the identificationcode C₁ for the radio zone 62 ₁. However, if the mobile station (65 ₁-65_(N)) is capable of identifying the relative order of priority of theradio zone 62 ₁ with respect to other radio zones (for example, themicrocell 63 and the picocell 64), or if it is evident that the mobilestation (65 ₁-65 _(N)) should be set up for a wait in the radio zone atthe top of the hierarchy or the radio zone at the bottom thereof, theorder of priority may not be included in the announcement information.Accordingly, the volume of the announcement information is reduced sothat the system flexibility with respect to modifications etc. thereofcan be improved.

A description will now be given, with reference to FIGS. 1 and 11, ofthe operation of the system according to an embodiment that correspondsto the invention described in claims 8 and 9. For the sake of simplicityof the description that follows, it is assumed that the mobile station65 ₁ is located in the same location assumed in the description of therelated art.

In the absence of overlap zones such as a microcell 63, a picocell 64and the like at respective locations in a radio zone formed by the radiobase station 61 ₁, the base station control device 69 ₁ of the radiobase station 61 ₁ transmits the announcement information having the sameformat as that of the conventional announcement information as shown inFIG. 2, via the transmission and reception unit 68 ₁, the common antennaequipment unit 67 ₁ and the antenna 66 ₁.

If there are overlap zones, the base station control device 69 ₁ isprovided by a control station (not shown) with an identification code C₁and an associated order of priority P₁ for a control channel formed bythe radio base station 61 ₁, identification codes C₃ and C₄ for overlapcontrol channels assigned to the microcell 63 and the picocell 64embodying the overlap zones, the order of the identification codes C₃and C₄ not being related to the associated orders of priority. Theresultant series of identification information P₁, C₁, C₄ and C₃incorporated in the announcement information is indicated by a hatchedarea in FIG. 13. The wait enabled level and the wait disabled level arealso included in the announcement information as in the conventionalsystem. For the sake of simplicity of the description, it is assumedthat the order of priority P₁=0.

The control unit 77 ₁ of the mobile station 65 ₁ effects the measurementprocess and the zone determination process as in the conventionalsystem. In the zone determination process, a determination is made as towhether the format of the announcement information received via thecontrol channel in which the electric field intensity L₂ is measured isthe same as the conventional format shown in FIG. 2, depending onwhether the above-described series of the identification information isincluded in the announcement information ((1) of FIG. 11).

If the format of the announcement information is found to be the same asthe conventional format, the control unit 77 ₁ performs the zonedetermination process in accordance with the same procedure as observedin the conventional system before proceeding to a wait state ((2) ofFIG. 11).

If the format of the announcement information is not found to be thesame as the conventional format, the control unit 77 ₁ extracts theorder of priority P₁ and the identification code C₁ from the series ofidentification information P₁, C₁, C₄ and C₃ and stores the extractedinformation in the selected candidate zone register in the main memory((3) of FIG. 11). The control unit 77 ₁ measures the electric fieldintensity L₂ of the overlap control channels specified by theidentification codes C₄ and C₃ and stores the identification codes C₄and C₃, and the orders of priority thereof in the selected candidatezone register. A similar step as above is performed in the event thatany additional identification code is received in the form of theannouncement information (an identification code that is repeated is notsubject to the above step).

When the identification codes and the associated orders of priority forthe radio zones that are candidates for a wait zone have been stored inthe selected candidate zone register, the control unit 771 performs thesame steps ((a), (4)-(9) of FIG. 11) as performed in the embodiment thatcorresponds to the invention described in claims 4-7, before proceedingto a wait state.

According to the embodiment described above, the announcementinformation may not include the orders of priority of all the microcellsand picocells in order for the control unit 77 ₁ of the mobile station65 ₁ to specify the control channel for the radio zone in which themobile station 65 ₁ is actually located before proceeding to a waitstate.

Therefore, an advantage of the embodiment that corresponds to theinvention described in claims 8 and 9 over the embodiment thatcorresponds to the invention described in claims 4-7 is that thetransmission efficiency of the control channel is increased andflexibility with respect to different modes of service is available.

While the identification codes in the foregoing embodiments are foridentifying individual control channels or overlap control channels, thepresent invention is not limited to such a constitution. The mobilestation (65 ₁-65 _(N)) may use alternative identification information(zone identification information) for identifying radio zones (such asthe picocell 64, the microcell 63, the radio zone 62 ₁), instead ofcontrol channels associated therewith, included in the announcementinformation, in order to determine a radio zone for entry.

In the alternative approach described above, information specifyingoverlap control channels and control channels that correspond to thezone identification information may be stored in the form of a table inan area reserved in a main memory of the control unit 77 ₁-77 _(N), ormay be provided separately (for example, as part of the announcementinformation) in accordance with the radio channel setting controlexecuted in relation to the radio base stations 61 ₁-61 ₄.

FIG. 14 is a flowchart of an operation of the mobile communicationsystem according to an embodiment that corresponds to the inventiondescribed in claims 10, 14 and 15.

A description will now be given, with reference to FIGS. 1 and 14, ofthe operation according to an embodiment that corresponds to theinvention described in claim 10. For the sake of simplicity of thedescription that follows, it is assumed that the mobile station 65 ₁ islocated in the same location assumed in the description of the relatedart.

In the absence of overlap zones at respective locations in a radio zoneformed by the radio base station 61 ₁, the base station control device69 ₁ of the radio base station 61 transmits the announcement informationhaving the same format as that of the conventional announcementinformation as shown in FIG. 2, via the transmission and reception unit68 ₁, the common antenna equipment unit 67 ₁ and the antenna 66 ₁.

If there are overlap zones, the base station control device 69 ₁ isprovided by a control station (not shown) with an identification code C₁for a control channel assigned to the radio base station 61 ₁,identification codes C₃ and C₄ for overlap control channels assigned tothe microcell 63 and the picocell 64 embodying the overlap zones, ordersof priority P₁, P₃ and P₄ indicating the hierarchical order of the radiozone 62 ₁, the microcell 63 and the picocell 64, wait enabled levelsL_(th1), L_(th2) and L_(th3) and the wait disabled levels l_(th1),l_(th3) and l_(th4), via the communication link 71 ₁ and thetransmission device 70 ₁. For the sake of simplicity of the description,it is assumed that the radio zone 62 ₁ has the order of priority P₁=0,the microcell 63 P₃=1 and the picocell 64 P₄=2.

As indicated by a hatched area in FIG. 15, the base station controldevice 69 ₁ incorporates, in the announcement information, the orders ofpriority P₁, P₃ and P₄, the identification codes C₁, C₃ and C₄, the waitenabled levels L_(th1), L_(th2) and L_(th3) and the wait disabled levelsl_(th1), l_(th3) and l_(th4), resulting in series of identificationinformation (P₁, C₁, L_(th1) and l_(th1)) . . . (P₄, C₄, L_(th4) andl_(th4)) each corresponding to the radio zone.

The control unit 77 ₁ of the mobile station 65 ₁ effects the measurementprocess and the zone determination process as in the conventionalsystem. In the zone determination process, a determination as to whetherthe format of the announcement information received via the controlchannel subject to the measurement of the electric field intensity L₂ isthe same as the conventional format shown in FIG. 2 is made, dependingon whether the above-described series of the identification informationis included in the announcement information ((1) of FIG. 14).

If the format of the announcement information is found to be the same asthe conventional format, the control unit 77 ₁ performs the zonedetermination process in accordance with the same procedure as observedin the conventional system before proceeding to a wait state ((2) ofFIG. 14).

If the format of the announcement information is not found to be thesame as the conventional format, the control unit 77 ₁ stores the seriesof the identification information (P₁, C₁, L_(th1) and l_(th1)) . . .(P₄, C₄, L_(th4) and l_(th4)) included in the announcement informationin the selected candidate zone register (A) of FIG. 14). The controlunit 77 ₁ sorts the combinations of the orders of priority, theidentification codes, the wait enabled levels and the wait disabledlevels stored in the selected candidate zone register, in the ascendingorder of priority. Once this sorting is done, all the orders of priorityare removed from the register ((a) of FIG. 14), resulting in the seriesof identification information consisted of the identification codes, thewait enabled levels and the wait disabled levels being stored in theselected candidate zone register.

The control unit 77 ₁ sequentially refers to the identification codesC₄, C₃ and C₁, and wait enabled levels L_(th4), L_(th3) and L_(th1)arranged in the ascending order of priority so as to measure theelectric field intensity L₃ of the overlap control channels and thecontrol channel corresponding to the respective identification codes((4) of FIG. 14). The control unit 77 ₁ then compares the measuredelectric field intensity with the wait enabled level L_(th) thatcorresponds to the measured channel ((5) of FIG. 14).

When the result of the comparison is available, the control unit 77 ₁then enters a wait state in accordance with the same procedure observedin the embodiment that corresponds the invention described in claim 4.The steps subsequent to (5) of FIG. 14 are designated by the samereference numerals (6)-(9) as the corresponding steps of FIG. 9, and thedescription thereof is omitted.

According to the embodiment that corresponds to the invention describedin claim 10, the mobile stations 65 ₁-65 _(N) give a priority to theradio zone having a greater order of priority, in selecting a wait zone.The threshold level of the electric field intensity that serves as acriteria associated with each radio zone for selection of the wait zonecan be dynamically (or statically) set under the control of the radiobase station.

Accordingly, the geographical distribution (number) of the mobilestations set up for a wait in the radio zones 62 ₁ and 62 ₂, themicrocell 63 and the picocell 64 can be properly established. Also, thehierarchy of radio zones can be properly established. As in theembodiment that corresponds to the invention described in claim 2, themobile stations 65 ₁-65 _(N) can give a priority to the microcell 63over the radio zone 62 ₁ and give a priority to the picocell 64 over themicrocell 63, in selecting a wait zone.

While the embodiment described above is constructed such that the seriesof information (P₁, C₁, L_(th1) and l_(th1)) . . . (P₄, C₄, L_(th4) andl_(th4)) is sorted according to the ascending order (the descendingorder) of the order of priority, so that the identification codes, thewait enabled levels and the wait disabled levels are retained in theregister, the orders of priority may not be removed from the registerand may be referred to in selecting a wait zone.

FIG. 16 is a flowchart of an operation of a system according to anembodiment that corresponds to the invention described in claims 11, 12,14 and 15.

A description will now be given, with reference to FIGS. 1 and 16, of anoperation of a mobile communication system according to an embodimentthat corresponds to the invention described in claims 11 and 12.

In the absence of overlap zones at respective locations in a radio zoneformed by the radio base station 61 ₁, the base station control device69 ₁ of the radio base station 61 ₁ transmits the announcementinformation having the same format as that of the conventionalannouncement information as shown in FIG. 2, via the transmission andreception unit 68 ₁, the common antenna equipment unit 67 ₁ and theantenna 66 ₁.

If there are overlap zones, the base station control device 69 ₁ isprovided by a control station (not shown) with an identification code C₁for a control channel formed by the radio base station 61 ₁,identification codes C₃ and C₄ for overlap control channels assigned tothe microcell 63 and the picocell 64 embodying the overlap zones, ordersof priority P₁, P₃ and P₄ indicating the hierarchical order of the radiozone 62 ₁, the microcell 63 and the picocell 64, corrected values Δ₁, Δ₂and Δ₃ indicating the enabled levels in the form of relative levels withrespect to a predetermined reference level L₀ and the wait disabledlevels l_(th1), l_(th3) and l_(th4), via the communication link 71 ₁ andthe transmission device 70 ₁. For the sake of simplicity of thedescription, it is assumed that the radio zone 62 ₁ has the order ofpriority P₁=0, the microcell 63 P₃=1 and the picocell 64 P₄=2.

As indicated by a hatched area in FIG. 17, the base station controldevice 69 ₁ incorporates, in the announcement information, theidentification codes C₁, C₃ and C₄, the orders of priority P₁, P₃ andP₄, the corrected values Δ₁, Δ₂ and Δ₃ and the wait disabled levelsl_(th1), l_(th3) and l_(th4), resulting in series of identificationinformation (P₁, C₁, Δ₁ and l_(th1)) . . . (P₄, C₄, Δ₄ and l_(th4)) eachcorresponding to the radio zone.

The control unit 77 ₁ of the mobile station 65 ₁ effects the measurementprocess and the zone determination process as in the conventionalsystem. In the zone determination process, a determination as to whetherthe format of the announcement information received via the controlchannel subject to the measurement of the electric field intensity L₂ isthe same as the conventional format shown in FIG. 2 is made, dependingon whether the above-described series of the identification informationis included in the announcement information ((1) of FIG. 16). If theformat of the announcement information is found to be the same as theconventional format, the control unit 77 ₁ performs the zonedetermination process in accordance with the same procedure as observedin the conventional system before proceeding to a wait state ((2) ofFIG. 16).

If the format of the announcement information is not found to be thesame as the conventional format, the control unit 77 ₁ stores the seriesof the identification information (P₁, C₁, Δ₁ and l_(th1)) . . . (P₄,C₄, Δ₄ and l_(th4)) included in the announcement information in theselected candidate zone register. The control unit 77 ₁ sorts thecombinations of the orders of priority, the identification codes, thecorrected values and the wait disabled levels stored in the selectedcandidate zone register, in the ascending order of priority. Once thissorting is done, all the orders of priority are removed from theregister, resulting in the series of identification informationconsisted of the identification codes, the corrected values and the waitdisabled levels being stored in the selected candidate zone register((A) of FIG. 16).

The control unit 77 ₁ sequentially refers to the identification codesC₄, C₃ and C₁, and corrected values Δ₁, Δ₂ and Δ₃ arranged in theascending order of priority so as to measure the electric fieldintensity L₃ of the overlap control channels and the control channelcorresponding to the respective identification codes ((4) of FIG. 16).The control unit 77 ₁ then compares the measured electric fieldintensity with a sum of the corrected value A for the measured channeland the reference value L₀ ((5) of FIG. 16).

When the result of the comparison is available, the control unit 77 ₁then enters a wait state in accordance with the same procedure observedin the embodiment that corresponds to the invention described in claim4. The steps subsequent to (5) of FIG. 16 are designated by the samereference numerals (6)-(9) as the corresponding steps of FIG. 14, andthe description thereof is omitted.

According to the embodiment described above, the corrected valuessmaller than the values of the wait enabled levels are included in theannouncement information in place of the wait enabled levels. The mobilestations 65 ₁-65 _(N) can give a priority to the radio zone having agreater order of priority, in selecting a wait zone.

Accordingly, the transmission efficiency of the control channel can bemaintained at a high level. The geographical distribution (number) ofthe mobile stations set up for a wait in the radio zones 62 ₁ and 62 ₂,the microcell 63 and the picocell 64 can be properly established. Also,the hierarchy of radio zones can be properly established. The mobilestations 65 ₁-65 _(N) can give a priority to the microcell 63 or thepicocell 64 over the radio zone 62 ₁, in selecting a wait zone.

While the embodiment described above is constructed such that the seriesof information (P₁, C₁ Δ₁ and l_(th1)) . . . (P₄, C₄, Δ₄ and l_(th4)) issorted according to the ascending order (the descending order) of theorder of priority so that the identification codes, the corrected valuesand the wait disabled levels are retained in the register, the orders ofpriority may not be removed from the register and may be referred to inselecting a wait zone.

The embodiment described above is constructed such that the radio basestation transmits the corrected values associated with all themicrocells and picocells formed within the radio zone of that radio basestation. Alternatively, for example, the radio base stations eachforming the radio zone, the microcell or the picocell may transmit onlythe corrected value associated with its own radio zone. In such a case,the mobile station is expected to perform the determination step ((5) ofFIG. 16) by acquiring the corrected value from the individual controlchannels subject to measurement of the electric field intensity.

Although no description is given of a process related to the waitdisabled level in the embodiments that correspond to the inventiondescribed in claims 10-12, the wait disabled level may be employed as acriteria in a conventional determination for determining whether or notthe mobile station should exit a wait state.

Previous to the determination process, the mobile station may remove,from the selected candidate zone register, wait disabled levels otherthan that of the control channel (or the overlap control channel) inwhich the mobile station is set up for a wait.

In the foregoing embodiments, comparison of the measured electric fieldintensity with the wait enabled level is conducted in the ascendingorder of priority assigned to the control channels that are specified bythe identification codes stored in the candidate zone register or theselected candidate zone register, so that the control channel (or theoverlap control channel) for which it is found that the measuredelectric field intensity exceeds the wait enabled level is selected asthe control channel in which to wait. Alternatively, the electric fieldintensity of the control channels is first measured irrespective of theorder of priority thereof, and then comparisons are made in theascending order of priority.

FIG. 18 is a flowchart of an operation of a mobile communication systemaccording to an embodiment that corresponds to the invention describedin claims 13-15.

A description will now be given, with reference to FIGS. 1 and 17, of anoperation of a mobile communication system according to an embodimentthat corresponds to the invention described in claim 13.

The inventive feature of this system consists in the measuring process.The other processes including the zone entry process are the same as thecorresponding processes in the embodiments described so far, and thedescription thereof is omitted.

Those processes of FIG. 18 that are identical to the correspondingprocesses of FIG. 3 are designated by the same reference numerals, andthe description thereof is omitted.

Upon a power-on, the control unit 77 ₁ of the mobile station 65 ₁measures sequentially the electric field intensity L₁ of the controlchannels registered in the control table channel by controlling thetransmission and reception unit 74 ₁ ((1) of FIG. 18). A determinationis then made as to whether or not the measured electric field intensityis greater than a predetermined threshold level L_(th) ((2) of FIG. 18).

The control unit 77 ₁ registers the control channels for which adetermination that the measured electric field intensity is greater thanthe threshold level L_(th) is obtained, in the candidate zone register,in relation to the electric field intensity ((3) of FIG. 18).

The control unit 77 ₁ starts the zone entry determination processwithout measuring the electric field intensity of the other controlchannels registered in the control channel table.

In those steps of the zone entry determination process which steps arestarted when it is found that the format of the announcement informationdiffers from the conventional format, all the control channels,specified by the identification information provided in the order ofpriority or provided coupled to information indicating the respectiveorder of priority, are subject to the measurement of the electric fieldintensity and also to the comparison for determining whether or not themeasured electric field intensity exceeds the wait enabled level.

According to the embodiment described above, the time required for themobile station (65 ₁-65 _(N)) to enter a wait state upon a power-on isreduced. Therefore, it is ensured that the service can be providedpromptly upon a power-on or upon an exchange of a battery.

A description will now be given, with reference to FIGS. 1, 9, 11, 14,16 and 18, of an operation of a mobile communication system according toan embodiment that corresponds to the invention described in claims 14and 15.

The difference between this embodiment and the earlier embodimentsconsists in the measurement process and the zone determination process.

In the measurement process according to this embodiment, the controlunit 77 ₁ allows the previously measured electric field intensity for agiven channel to be stored in the candidate zone register in relation toits electric field intensity.

In further accordance with this embodiment, when the control unit 77 ₁measures the electric field intensity L₂ or L₃ ((7) of FIG. 3, (4) ofFIG. 9, (4) of FIG. 11, (4) of FIGS. 14 and (4) of FIG. 16), adetermination is made as to whether or not the control channel subjectto the measurement is stored in the candidate zone register. If anaffirmative answer is given in the determination, the measurement ofthat control channel is omitted. The electric field intensity alreadystored in the target zone register for that control channel is regardedas the electric field intensity L₂ or L₃.

According to the above-described embodiment, it is possible to reducethe total number of control channels to be subjected to the measurementof its electric field intensity before the mobile station enters a waitstate. Therefore, the operating efficiency of the mobile station isincreased and the quality of the service is improved.

As shown in FIGS. 9, 10, 13 and 15, according to the foregoingembodiments, a determination as to whether or not the electric fieldintensity exceeds the wait enabled level is made for the controlchannels that correspond to all the identification codes stored in theselected candidate zone register. An alternative approach indicated bythe chain lines in FIGS. 9, 10, 13 and 15 is that upon a determinationthat the electric field intensity of any channel (radio zone) exceedsthe wait enabled level, the mobile station immediately is set up for await in that control channel (radio zone) so that the mobile station canreceive the communication service.

While the identification information for overlapping zones adjacent tothe radio zone formed by a given radio base station is not transmittedby the given radio base station, according to the foregoing embodiments,the identification information for the adjacent zones may be transmittedas long as the relative orders of priority of the adjacent radio zoneswith respect to the radio zone formed by the given radio base stationare recognized properly by the mobile station.

In the foregoing embodiments, various information is arranged in theannouncement information in the ascending order of priority, theannouncement information is not limited to such a construction. Forexample, the various information may be arranged in the descending orderor in a predetermined format corresponding to the order of priority.

Also, in the foregoing embodiments, the announcement informationincludes the channel numbers of the control radio channels assigned tothe respective radio zones (radio base stations) and used to transmitthe announcement information. However, the channel numbers may bereplaced by a radio frequency in case the radio channel is formed by asingle radio frequency as in the case of an analog mobile communicationsystem, instead of being constituted according to a time division systemsuch as the TDMA system.

Further, in the foregoing embodiments, digital transmission of theannouncement information is effected by utilizing a spare field notreserved under a given frame format, the present invention is notlimited to such a construction. For example, if the size of the sparefield is not satisfactorily large, the announcement information may betransmitted in multiframes. The announcement information may betransmitted in a plurality of frames, either frame by frame or individends thereof, as long as the mobile station can properly receivethe announcement information.

While the foregoing embodiments are constructed such that theannouncement information is transmitted via the control radio channel,the present invention can be applied to various systems irrespective ofthe radio channel setting control method and the radio transmissionmethod.

Reference is made to FIG. 20 and a description will now be given ofembodiments of the invention directed to resolving the second aspect ofthe problem with the conventional mobile communication system. Accordingto the invention described below, each of a plurality of base stationsforming overlapping zones and constituting a mobile communication systemis assigned an order of priority. A mobile station requests a messagechannel from the base station having a relatively high order of priorityso that a call using that base station is enabled.

Referring to FIG. 20, a zone 221 formed by a base station 201 and a zone222 formed by a base station 202 are adjacent to each other. In the zone221 are provided a base station 203 having a smaller transmission powerthan the base station 201 and forming a zone 223 and a base station 204having a smaller transmission power than the base station 203 andforming a zone 224 smaller than the zone 223. A mobile station 205 ismovable in an area comprising the zone 221, the zone 222, the zone 223and the zone 224.

FIG. 32 shows a hardware construction of a base station assumed in thefollowing description, and FIG. 33 shows a hardware construction of amobile station assumed in the following description.

Referring to FIG. 32, a transmission/reception unit 101 of a basestation includes TRX shelves 106, an RF distribution/synthesis unit 107,an amplifier unit 108 and an antenna 108. A control unit 102 managesannouncement information set up in the base station by a control center104 via an interface unit 103. The control unit 102 transmits theannouncement information to a transmitter/receiver (TRX) within the TRXshelf 106 at a timing provided by the oscillator 105. Thetransmitter/receiver which has received the announcement informationtransmits the announcement information to the mobile station via the RFdistribution/synthesis unit 107, the amplifier unit 108 and the antenna109.

A request for a message channel issued by the mobile station originatinga call or receiving a call is received by the transmitter/receiver inthe TRX shelf 106 via the antenna 109, the amplifier unit 108 and the RFdistribution/synthesis unit 107. The information received by thetransmitter/receiver is transmitted to the control center 104 under thecontrol of the control unit 102 so that communication via the fixednetwork 105 is set up. By definition, a shelf is a box for storing thetransmitter/receiver.

The transmission/reception unit 101 corresponds to atransmission/reception unit 306 shown in FIG. 19 illustrating theprinciple of the present invention directed to resolving the secondaspect of the problem with the conventional mobile communication system.The control unit 102 corresponds to a data control unit 307 shown inFIG. 19. The description of the transmission/reception unit 306 and thedata control unit 307 will be given later.

Referring to FIG. 33, a transmission/reception unit 501 of a mobilestation includes a TDMA (time division multiple access) circuit 504, amodulator 510, a demodulator 503, receivers 508 and 509, a commonantenna 507, and antennas 505 and 506. The announcement information fromthe base station is received by the receiver 508 via the antenna 505 orreceived by the receiver 509 via the antenna 506 and the common antenna507. The signal demodulated by the demodulator 503 is processed by theTDMA circuit 504. The control unit 502 selects the base station fromwhich the mobile station is to request a message channel, based on theorder of priority of the base stations contained in the announcementinformation and based on the reception level in the perch channelsprovided for the respective base station.

A request for a message channel occurring when a call is originated orwhen a call is received is transmitted to the TDMA circuit 504 under thecontrol of the control unit 502. The request is processed by the TDMAcircuit 504 and then modulated by the modulator 510. The modulatedrequest is transmitted to the target base station via the common antenna507 and the antenna 506.

The transmission/reception unit 501 corresponds to an announcementinformation receiving unit 309 and a transmission unit 310 describedlater. The control unit 502 corresponds to a message channel controlunit 308, an announcement information storage unit 311 and a receptionlevel measuring unit 312 described later.

FIG. 19 illustrates the principle of the present invention directed toresolving the second aspect of the problem with the conventional mobilecommunication system. The base station 201 includes the data controlunit 307 and the transmission/reception unit 306. The base station 201transmits announcement information to mobile stations and assigns amessage channel to a requesting mobile station.

The data control unit 307 manages and controls the order of priorityassigned to the base station 201 and other base stations associated withthe base stations 201. The data control unit 307 also controlsassignment of a message channel responsive to a request for a messagechannel from a mobile station, so as to set up a call. A request for amessage channel could occur when switching from one message channel toanother occurs during a communication. A request for a message channelcould also occur when a mobile station originates a call or receives acall. The transmission/reception unit 306 provides an interface for allthe signals controlled by the data control unit 307. The base stations202, 203 and 204 have the same construction and function the same way asthe base station 201 so that the description thereof is omitted.

Referring again to FIG. 19, a mobile station 205 comprises the messagechannel control unit 308, the announcement information receiving unit309, the transmission unit 310, the announcement information storageunit 311 and the reception level measuring unit 312.

The message channel control unit 308 operates to select a base stationto which a request for a message channel is to be issued, based on theorder of priority of the base stations included in the announcementinformation from the base station (one of the base stations 201, 202,203 and 204), and based on the reception level in the perch channelsprovided for the respective base stations (the base stations 201, 202,203 and 204). The announcement information receiving unit 309 operatesto receive the announcement information from the base station. Thetransmission unit 310 operates to transmit a request for a messagechannel to the base station selected by the message channel control unit308. The announcement information storage unit 311 stores theannouncement information received by the announcement informationreceiving unit 309. The reception level measuring unit 312 reads theannouncement information stored in the announcement information storageunit 311 when a request for a message channel is issued to the basestation, and measures the reception level of the perch channels providedfor the respective base stations in the descending order of prioritysuch that the reception level in the perch channel having the highestpriority is measured first. The reception level measuring unit 312transmits the measured reception level to the message channel controlunit 308.

FIGS. 21A and 21B illustrate the principle according to which a mobilestation issues a request for a message channel to a base station in themobile communication system of FIG. 19. FIG. 21A shows how theannouncement information is delivered, and FIG. 21B shows the principleof the flow of the call origination operation according to the presentinvention.

An outline of the call request operation according to the presentinvention will now be given. It is assumed that the mobile station 205is located in the service area formed by the base station 204 but is setup for a wait in the base station 201. When the mobile station 205issues a call, the reception level measuring unit 312 of the mobilestation 205 measures the reception level of the base stations 201, 202,203 and 204 and determines that the announcement information is to bereceived from, for example, the base station 201 that provides thehighest reception level. It is assumed that the reception levelsmeasured by the reception level measuring unit 312 are such that thebase station 201, the base station 202, the base station 203, the basestation 204 and the base station 202 have increasingly lower receptionlevels in the stated order.

When the transmission/reception unit 306 of the base station 201transmits the announcement information managed by the data control unit307, the announcement information receiving unit 307 of the mobilestation 205 stores the received announcement information in theannouncement information storage unit 311. The announcement informationtransmitted by the base station could have the format as shown in FIG.22, FIG. 23 or FIG. 24. The announcement information having the formatof FIG. 22 includes the order of priority assigned to the base stationtransmitting the announcement information. The format shown in FIG. 23is such that the perch channel codes corresponding to the base stationwhich is the source of the announcement information and corresponding tothe adjacent base stations are arranged in the descending order (or theascending order) of the priority. The format shown in FIG. 24 is suchthat each of the perch channel codes corresponding to the source basestations and the adjacent base stations is coupled to the associatedorder of priority.

The reception level measuring unit 312 of the mobile station originatinga call measures the reception level of the perch channels provided forthe base stations, in the descending order of the priority based onorder of priority specified in the announcement information from thebase station (step S1). The reception level measuring unit 312 transmitsthe reception level to the message channel control unit 308. It isassumed that the order of priority is such that the base station 204,the base station 203, the base station 201 and the base station 202 haveincreasingly lower priorities in the stated order.

Once the reception level in the perch channel corresponding to the basestation 204 is received, the message channel control unit 308 determinesthat a request for a message channel is to be issued to the base station204 if the measured reception level is equal to or exceeds apredetermined threshold level. The message channel control unit 308 thenissues a request for a message channel to the base station 204 via thetransmission unit 310 (S2).

A detailed description of call origination outlined above will now begiven. FIG. 25 is a flowchart showing the flow of the call originationoperation, and FIG. 26 shows a sequence of the call originationoperation.

The reception level measuring unit 312 of the mobile station 205measures the reception level provided by the base stations (the basestations 201, 202, 203 and 204) forming the respective zones (stepsS201, S202, S203 and S204 of FIG. 26). It is assumed that the measuredreception levels are such that the base station 202, the base station204, the base station 203 and the base station 201 have increasinglyhigher reception levels in the stated order. Accordingly, the messagechannel control unit 308 determines that the announcement information isto be received from the base station 201.

Upon receipt of the announcement information from the base station 201(S205), the announcement information receiving unit 309 of the mobilestation 205 causes the announcement information to be stored in theannouncement information storage unit 311. The announcement informationcould have the format as shown in FIG. 22, FIG 23 or FIG. 24. Theannouncement information having the format of FIG. 22 includes the orderof priority assigned to the base station transmitting the announcementinformation. When the mobile station 205 receives the announcementinformation having the format as shown in FIG. 22, the mobile station205 needs to acquire the announcement information from the base stationsother than the source base station (the base station 201) thattransmitted the announcement information, in order to learn the order ofpriority assigned to the base stations adjacent to the source basestation. The format shown in FIG. 23 is such that the perch channelcodes corresponding to the source base station and the adjacent basestations are arranged in the descending order (or the ascending order)of the priority. The format shown in FIG. 24 is such that each of theperch channels codes corresponding to the source base stations and theadjacent base stations is coupled to the associated order of priority.It will now be assumed that the mobile station 205 has received theannouncement information having the format of FIG. 23.

The message channel control unit 308 reads the announcement informationfrom the announcement information storage unit 311 so as to learn theorder of priority assigned to the base stations (the base stations 201,202, 203 and 204) and a predetermined level of the reception level thatenables a request for a message channel. It is assumed that the basestation 202, the base station 201, the base station 203 and the basestation 204 have the increasingly higher priorities. The reception levelmeasuring unit 312 reads the announcement information from theannouncement information storage unit 311 so as to retrieve the order ofpriority included in the announcement information to be assigned to therespective perch channels codes, each of the perch channel codescorresponding to the associated base station. The reception levelmeasuring unit 312 then measures the reception level of the perchchannel corresponding to the base station 204 having the highestpriority (S206).

The reception level measuring unit 312 transmits the measured receptionlevel to the message channel control unit 308. The message channelcontrol unit 308 determines whether the level is equal to or exceeds apredetermined threshold level that enables a request for a messagechannel. If it is determined that level is equal to or exceeds thethreshold level, the mobile station acquires the announcementinformation from the base station 204 (S207). If it is determined thatthe level is below the threshold level, the reception level measuringunit 312 measures the reception level of the perch channel correspondingto the base station 203 having the next highest order of priority(S206). The reception level measuring unit 312 repeats step S206 suchthat it successively measures the reception level of the perch channelprovided for the respective base stations in the descending order ofpriority, until the base station that provides the reception level whichis equal to or exceeds the threshold level is found, or until all theperch channels are subject to measurement.

When the user of the mobile station 205 performs an operation fororiginating a call (S208 in FIGS. 26 and S101 in FIG. 25) after S207,the message channel control unit 308 determines whether the announcementinformation from the base station 204 contains the order of priority ofthe base stations (base stations 201, 202, 203 and 204) (S102).

When the announcement information contains the order of priority (YES inS102) of the base stations 201, 202, 203 and 204, the reception levelmeasuring unit 312 reads the announcement information from theannouncement information storage unit 311 so as to retrieve the order ofpriority assigned to the perch channels which are provided for the basestations 201, 202, 203 and 204. The reception level measuring unit 312measures the reception level of the perch channel corresponding to thebase station 204 having the highest priority. The order of prioritystored in the announcement information storage unit 311 is such that thebase station 202<the base station 201<the base station 203<the basestation 204.

The reception level measuring unit 312 transmits the reception level inthe perch channel corresponding to the base station 204 to the messagechannel control unit 308. The message channel control unit 308determines whether the reception level is equal to or exceeds apredetermined threshold level that enables a request for a messagechannel (S103). If the message channel control unit 308 determines thatthe reception level is equal to exceeds the threshold level (YES inS103), the message channel control unit 308 retrieves restrictioninformation from the announcement information transmitted from the basestation 204 and stored in the announcement information storage unit 311.The message channel control unit 308 determines whether it is possibleto originate a call in a zone 224 (see FIG. 20).

If the message channel control unit 308 determines in step S103 that thereception level is below the threshold level (NO in S103), the receptionlevel measuring unit 312 determines whether a perch channelcorresponding to the base station having the next highest priority isavailable (S104). If no perch channel corresponding to the base stationhaving the next highest priority is available (No in S104), it isdetermined that the mobile station 205 cannot originate a call (S105)and is put in a wait state (S106). If a perch channel corresponding tothe base station having the next highest priority is available (YES inS104), the reception level measuring unit 312 repeats steps S104 andS107 such that it successively measures (NO in S107) the reception levelin the perch channels in the descending order of priority until the basestation providing a reception level which is equal to or exceeds thethreshold level is found (YES in S107) or until all the perch channelshave been subject to measurement (NO in S104). If the message channelcontrol unit 308 finds a base station that provides a reception levelwhich is equal to or exceeds the threshold level (YES in S107), themessage channel control unit 308 retrieves the restriction informationfrom the announcement information stored in the announcement informationstorage unit 311 so as to determine if it is possible to originate acall in the zone formed by the base station found in S107 (S108). If itis determined that the order of priority of the base stations is notincluded in the announcement information (NO in S102), the messagechannel control unit 308 retrieves the restriction information from theannouncement information stored in the announcement information storageunit 311 and determines whether it is possible to originate a call inthe zone formed by the base station which is the source of the storedannouncement information (S108).

If it is determined that call origination is disabled in the zone 224formed by the base station 204 (NO in S108), the mobile station 205 isput in a wait state (S109). If call origination is enabled (YES inS108), the message channel control unit 308 retrieves the restrictioninformation from the announcement information stored in the announcementinformation storage unit 311 so as to determine whether a restrictionregarding a preferred mobile station is imposed on the zone 224 formedby the base station 204 (S110). A preferred mobile station is a stationwhich is given a precedence in message channel assignment.

If it is determined that a restriction regarding a preferred mobilestation is imposed (YES in S110) and if the mobile station 205 is apreferred mobile station (YES in S111), the message channel control unit308 determines whether call origination in the mobile station 205 isenabled (S112). If it is determined that call origination is enabled(YES in S112), the message channel control unit 308 determines that arequest for a message channel is to be issued to the base station 204and causes the transmission unit 310 to transmit a request for a messagechannel (S209). If it is determined that call origination is disabled(NO in S112), the mobile station 205 is put in a wait state (S113).

If a restriction regarding a preferred mobile station is imposed (YES inS110) and if the mobile station 205 is not a preferred mobile station(NO in S111), the message channel control unit 308 determines whether arestriction is imposed on the mobile station 205 (S114). If there is norestriction (NO in S114), the message channel control unit 308determines that a request for a message channel is to be issued to thebase station 204 and causes the transmission unit 310 to transmit arequest for a message channel to the base station 204 (S209). If thereis a restriction (YES in S114), the mobile station 205 is put in a waitstate (S115).

If it is determined that no restriction regarding a preferred mobilestation is imposed (NO in S110), the message channel control unit 308determines that a request for a message channel is to be issued to thebase station 204 and causes the transmission unit 310 to transmit arequest for a message channel (S209).

When an unused message channel is available in the base station 204receiving the request for a message channel, the base station 204assigns a message channel to the mobile station 205 and transmits achannel assignment signal to the mobile station (S210). When there is nomessage channel available, the base station 204 notifies the mobilestation 205 that there is no message channel available, thus putting themobile station in a wait state.

The mobile station 205 that has received the channel assignment signaloriginates a call to another mobile station (S116) and establishes theassigned message channel with the base station 204 so as to start acall.

Referring to FIG. 20, a detailed description will now be given of how acall incoming to the mobile station 205 located in the service areaformed by the base station 203 and set up for a wait in the base station201 is processed according to the mobile communication system of thepresent invention. Reference is also made to FIG. 27, which shows theflow of the call-incoming operation according to the present invention,and FIG. 28, which shows the sequence of the call-incoming operation.

The reception level measuring unit 312 of the mobile station 205measures the reception level provided by the base stations 201, 202, 203and 204 forming the respective zones (steps S401, S402, S403 and S404 inFIG. 28). It is assumed that the reception levels provided by the basestations 201, 202, 203 and 204 are such that the base station 202< thebase station 204< the base station 203< the base station 201, so thatthe message channel control unit 308 determines that the announcementinformation is to be received from the base station 201 providing thehighest reception level.

The mobile station 205 has received the announcement information fromthe base station 201 (S405), the announcement information receiving unit309 causes the announcement information to be stored in the announcementinformation storage unit 311. The announcement information could havethe format as shown in FIG. 22, FIG. 23 or FIG. 24. The announcementinformation having the format of FIG. 22 includes the order of priorityassigned to the base station transmitting the announcement information.When the mobile station 205 receives the announcement information havingthe format as shown in FIG. 22, the mobile station 205 needs to acquirethe announcement information from the base stations other than thesource base station (the base station 201) that transmitted theannouncement information, in order to learn the order of priorityassigned to the base stations adjacent to the source base station. Theformat shown in FIG. 23 is such that the perch channel codescorresponding to the source base station and the adjacent base stationsare arranged in the descending order (or the ascending order) of thepriority. The format shown in FIG. 24 is such that each of the perchchannels code corresponding to the source base stations and the adjacentbase stations is coupled to the associated order of priority. It willnow be assumed that the mobile station 205 has received the announcementinformation having the format of FIG. 23.

The message channel control unit 308 reads the announcement informationfrom the announcement information storage unit 311 so as to learn theorder of priority assigned to the base stations (the base stations 201,202, 203 and 204) and a predetermined level of the reception level thatenables a request for a message channel. It is assumed that the basestation 202, the base station 204, the base station 201 and the basestation 203 have the increasingly higher priorities. The reception levelmeasuring unit 312 reads the announcement information from theannouncement information storage unit 311 so as to retrieve the order ofpriority included in the announcement information to be assigned to therespective perch channels codes, each of the perch channel codescorresponding to the associated base station. The reception levelmeasuring unit 312 then measures the reception level of the perchchannel corresponding to the base station 203 having the highestpriority (S406).

The reception level measuring unit 312 transmits the measured receptionlevel to the message channel control unit 308. The message channelcontrol unit 308 then determines whether the level is equal to orexceeds a predetermined threshold level that enables a request for amessage channel. If the message channel control unit 308 determines thatthe level is equal to or exceeds the threshold level, the mobile station205 acquires the announcement information from the base station 203(S407). The message channel control unit 308 obtains the order ofpriority of the base stations 201, 202, 203 and 204 from theannouncement information from the base station 203. If the messagechannel control unit 308 determines that the level is below thethreshold level, the reception level measuring unit 312 measures thereception level of the perch channel corresponding to the base station204 given the next highest priority (S406). The reception levelmeasuring unit 312 repeats step S406 such that it successively measuresthe reception level in the perch channels in the descending order ofpriority until the base station providing a reception level which isequal to or exceeds the threshold level is found or until all the perchchannels have been subject to measurement.

When there is an incoming call in the mobile station 205 after S407(S408, S409, S410, S411) (S301 in FIGS. 27), and when the order ofpriority of the base stations 201, 202, 203 and 204 is included in theannouncement information (YES in S302), the reception level measuringunit 312 reads the announcement information from the announcementinformation storage unit 311 so as to retrieve the order of priority ofthe base stations 201, 202, 203 and 204, the order of priority beingindicated by information assigned to each of the perch channelscorresponding to the respective base stations 201, 202, 203 and 204; Thereception level measuring unit 312 measures the reception level of theperch channel corresponding to the base station 203 having the highestpriority. The order of priority stored in the announcement informationstorage unit 312 is such that the base station 201< the base station204< the base station 201< the base station 203.

The reception level measuring unit 312 transmits the reception level ofthe perch channel corresponding to the base station 203 to the messagechannel control unit 308. The message channel control unit 308determines whether the reception level is equal to or exceeds apredetermined threshold level that enables a request for a messagechannel (S303). If the message channel control unit 308 determines thatthe reception level is equal to or exceeds the threshold level (YES inS303), the message channel control unit 308 retrieves restrictioninformation from the announcement information transmitted from the basestation 203 and stored in the announcement information storage unit 311so as to determine whether call incoming is enabled in the zone 223formed by the base station 203 (S308).

If the message channel control unit 308 determines in S303 that thereception level is below the threshold level (NO in S303), the receptionlevel measuring unit 312 determines whether the base station having thenext highest priority is available (S304). If no perch channelcorresponding to the base station having the next highest priority isavailable (NO in S304), call incoming in the mobile station 205 isdisabled (S305) so that the mobile station 205 is put in a wait state(S306). If the perch channel corresponding to the base station havingthe next highest priority is available (YES in S304), the receptionlevel measuring unit 312 repeats steps S304 and S307 such that itsuccessively measures (NO in S307) the reception level in the perchchannels in the descending order of priority until the base stationproviding a reception level which is equal to or exceeds the thresholdlevel is found (YES in S307) or until all the perch channels have beensubject to measurement (NO in S304). If the message channel control unit308 finds a base station that provides a reception level which is equalto or exceeds the threshold level (YES in S307), the message channelcontrol unit 308 retrieves the restriction information from theannouncement information stored in the announcement information storageunit 311 so as to determine if call incoming is enabled in the zoneformed by the base station found in S307 (S308). If it is determined inS302 that the order of priority of the base stations is not included inthe announcement information (NO in S302), the message channel controlunit 308 retrieves the restriction information from the announcementinformation stored in the announcement information storage unit 311 anddetermines whether call incoming is enabled in the zone formed by thebase station which is the source of the stored announcement information(S308).

If it is determined that call incoming is disabled in the zone 223formed by the base station 203 (NO in S303), the reception levelmeasuring unit 312 determines whether the perch channel corresponding tothe base station having the next highest priority is available (S304).If no perch channel corresponding to the base station having the nexthighest priority is available (NO in S304), call incoming in the mobilestation 205 is disabled (S305) so that the mobile station 205 is put ina wait state (S306). If the perch channel corresponding to the basestation having the next highest priority is available (YES in S304), thereception level measuring unit 312 repeats steps S304 and S307 such thatit successively measures (NO in S307) the reception level in the perchchannels in the descending order of priority until the base stationproviding a reception level which is equal to or exceeds the thresholdlevel is found (YES in S307) or until all the perch channels have beensubject to measurement (NO in S304). If the message channel control unit308 finds a base station that provides a reception level which is equalto or exceeds the threshold level (YES in S307), the message channelcontrol unit 308 retrieves the restriction information from theannouncement information stored in the announcement information storageunit 311 so as to determine if call incoming is enabled in the zoneformed by the base station found in S307 (S308).

If it is determined that call incoming is enabled in the zone 223 formedby the base station 203 (YES in S308), the message channel control unit308 retrieves the restriction information from the announcementinformation transmitted from the base station 203 and stored in theannouncement information storage unit 311 so as to determine whether arestriction regarding a preferred mobile station is imposed in the zone223 formed by the base station 203 (S309).

If there is a restriction regarding a preferred mobile station (YES inS309) and if the mobile station 205 is a preferred mobile station (YESin S310), the message channel control unit 308 determines whether callincoming is enabled in the mobile station 205 (S311). If call incomingis enabled (YES in S311), the message channel control unit 308determines that a request for a message channel is to be issued to thebase station 203 and causes the transmission unit 310 to transmit arequest for a message channel (S412). If call incoming is disabled (NOin S311), the mobile station 205 is put in a wait state (S312).

If there is a restriction regarding a preferred mobile station (YES inS309) and if the mobile station 205 is not a preferred mobile station(NO in S310), the message channel control unit 308 determines whether arestriction is imposed on the mobile station 205 (S313). If there is norestriction (NO in S313), the message channel control unit 308determines that a request for a message channel is to be issued to thebase station 203 and causes the transmission unit 310 to transmit arequest for a message channel (S412). If there is a restriction (YES inS313), the mobile station 205 is put in a wait state (S314).

If it is determined that there is no restriction regarding a preferredmobile station (NO in S309), the message channel control unit 308determines that a request for a message channel is to be issued to thebase station 203 and causes the transmission unit 310 to transmit arequest for a message channel (S412).

The base station 203 receiving the request assigns an unused messagechannel to the mobile station 205 and transmits a channel assignmentsignal thereto (S413). If no unused message channel is available, themobile station 205 is put in a wait state.

The mobile station receiving the message channel assignment signalreturns a response to an incoming call to the base station 203 (S309),establishes the assigned message channel with the base station 203 so asto start a call (S414).

Referring to FIG. 20, a detailed description will now be given of how aswitching from one message channel to another is performed in the eventof a handover. It is assumed that the mobile station 205 is located inthe service area formed by the base station 201 and making a call viathe base station 201. FIG. 29 shows the flow of a recall channelswitching operation, and FIG. 30 shows the sequence of the recallchannel switching operation. The message channel switching performedwhen a handover occurs during a conversation is also performed whenthere is a drop in the reception quality.

It is assumed that, while the mobile 205 is communicating with anothermobile station by establishing a message channel with the base station201 (S601 in FIG. 30), the reception level provided by the base station201 drops below a predetermined threshold level, necessitating ahandover by switching message channels (S602) (S501 in FIG. 29). Themessage channel control unit 308 determines whether the order ofpriority is included in the announcement information from the basestation 201 (S602). The announcement information obtained when themessage channel is set up with respect to the base station 201 andstored in the announcement information storage unit 311 specifies theorder such that the base station 201< the base station 202< the basestation 203< the base station 204.

If it is determined that the order of priority of the base stations 201,202, 203 and 204 is included in the announcement information (YES inS502), the reception level measuring unit 312 reads the announcementinformation from the announcement information storage unit 311 so as toretrieve the order of priority of the base stations 201, 202, 203 and204 corresponding to the perch channel codes included in theannouncement information having the format of, for example, FIG. 23. Thereception level measuring unit 312 measures the reception level in theperch channel corresponding to the base station 204 assigned the nexthighest priority (S603).

The reception level measuring unit 312 transmits the reception level inthe perch channel corresponding to the base station 204 to the messagechannel control unit 308. The message channel control unit 308determines whether the level is equal to or exceeds a predeterminedthreshold level that enables a request for a message channel (S503). Ifthe message channel control unit 308 determines that the level is equalto or exceeds the threshold level (YES in S503), the message channelcontrol unit 308 retrieves restriction information from the announcementinformation transmitted from the base station 204 and stored in theannouncement information storage unit 311 so as to determine whetherrecall is enabled in the zone 224 (S508).

If the message channel control unit 308 determines that the receptionlevel is below the threshold level (NO in S503), the reception levelmeasuring unit 312 determines whether the perch channel corresponding tothe base station having the next highest priority next to the basestation 204 is available (S504). If no perch channel corresponding tothe base station having the next highest priority is available (NO inS504), message channel switching in the mobile station 205 is disabled(S505). In this case, the mobile station 205 is disconnected or switchedback to the base station 201 (S506). If a perch channel corresponding tothe base station having the next highest priority next to the basestation 204 is available (YES in S504), the reception level measuringunit 312 repeats steps S504 and S507 such that it successively measures(NO in S307) the reception level in the perch channels in the descendingorder of priority until the base station providing a reception levelwhich is equal to or exceeds the threshold level is found (YES in S507)or until all the perch channels have been subject to measurement (NO inS504). If the message channel control unit 308 finds a base station thatprovides a reception level which is equal to or exceeds the thresholdlevel (YES in S507), the message channel control unit 308 retrieves therestriction information from the announcement information stored in theannouncement information storage unit 311 so as to determine if recallis enabled in the zone formed by the base station found in S507 (S508).If it is determined that the order of priority of the base stations isnot included in the announcement information (NO in S502), the messagechannel control unit 308 retrieves the restriction information from theannouncement information stored in the announcement information storageunit 311 so as to determine whether recall is enabled in the zone formedby the base station which is the source of the stored announcementinformation (S508).

If it is determined that recall is disabled in the zone 224 formed bythe base station 224 (NO in S504), message channel switching is disabledin the mobile station 205 so that the mobile station 205 is disconnected(S509). If recall is disabled (YES in S508), the message channel controlunit 308 retrieves the restriction information from the announcementinformation transmitted from the base station 204 and stored in theannouncement information storage unit 311 so as to determine whether arestriction regarding a preferred mobile station is imposed in the zone224 formed by the base station 204 (S510).

If there is a restriction regarding a preferred mobile station (YES inS510) and if the mobile station 205 is a preferred mobile station (YESin S511), the message channel control unit 308 determines whether recallis enabled in the mobile station 205 (S512). If it is determined thatrecall is enabled (YES in S512), the message channel control unit 308determines that a request for a message channel is to be issued to thebase station 204 and causes the transmission unit 310 to transmit arequest for a message channel (S604). If recall is disabled (NO inS512), message channel switching in the mobile station 205 is disabledso that the mobile station 205 is disconnected (S513).

If there is a restriction regarding a preferred mobile station (YES inS510) and if the mobile station 205 is not a preferred mobile station(NO in S511), the message channel control unit 308 determines whether arestriction is imposed on the mobile station 205 (S514). If there is norestriction (NO in S514), the message channel control unit 308determines that a request for a communication is to be issued to thebase station 204 and causes the transmission unit 310 to transmit arequest for a message channel (S604). If there is a restriction (YES inS514), message channel switching in the mobile station 205 is disabledso that the mobile station 205 is disconnected (S515).

If it is determined that no restriction regarding a preferred mobilestation is imposed (NO in S510), the message channel control unit 308determines that a request for a message channel is to be issued to thebase station 204 and causes the transmission unit 310 to transmit arequest for a message channel (S604) (S516).

The base station 204 receiving the request assigns an unused messagechannel to the mobile station 205 and transmits a channel assignmentsignal thereto (S605). If no unused message channel is available, themobile station 205 is disconnected.

The mobile station receiving the message channel assignment signalestablishes the assigned message channel with the base station 204 so asto continue a call (S606).

As described above, the present invention as applied to a mobilecommunication system having a hierarchical zone construction enables amobile station to issue a request for a message channel to a basestation that forms a smaller zone and provides a lower reception level,instead of a base station that forms a larger zone and provides a higherreception level. The present invention accomplishes such an arrangementby including in the announcement information the order of priorityassigned to each of the base stations constituting the hierarchical zoneconstruction.

The present invention is not limited to the above described embodiments,and variations and modifications may be made without departing from thescope of the present invention.

1. A mobile communication system comprising: a plurality of radio basestations forming respective radio zones and effecting a radio channelsetting control in accordance with a predetermined procedure; and amobile station selecting, as a wait zone, one of the radio zones thatsatisfies a criteria demanded by the predetermined procedure, andreceiving communication service via the selected wait zone, each of theradio base stations comprising: traffic control means for setting atraffic distribution for the plurality of radio zones; and announcingmeans for generating announcement information including the order ofpriority assigned to the plurality of radio zones, the order of prioritybeing assigned in accordance with a probability density given to each ofthe plurality of radio zones under the distribution set by the trafficcontrol means, and for transmitting announcement information to theradio zone formed by the radio station to which the announcing meansbelongs, the mobile station comprising: announcement informationreceiving means for receiving the announcement information transmittedby the announcing means in accordance with the predetermined procedure;and wait control means for selecting one of the radio zones as a waitzone, the radio zone to which a highest priority is assigned being afirst candidate for selection by the wait control means.
 2. A mobilecommunication system comprising: a plurality of radio base stationsforming one or a plurality of radio zones and one or a plurality ofsmall-scale radio zones, resulting in a hierarchy of overlapping radiozones, and effecting a radio channel setting control in accordance witha predetermined procedure; and a mobile station accessing one of theradio zones formed by the respective one of the plurality of radio basestations, in accordance with a predetermined procedure, and receivingcommunication service via the accessed radio zone, each of the pluralityof radio base stations comprising: announcing means for transmittingannouncement information which includes identification information foridentifying radio channels assigned to respective radio zones andsmall-scale radio zones, via the radio channel assigned to the radiozone formed by the radio base station to which the announcing meansbelongs, the identification information being arranged in theannouncement information so as to correspond to the hierarchy ofoverlapping radio zones, the mobile station comprising: announcementinformation receiving means for receiving the announcement informationtransmitted by the announcing means, in accordance with the procedurefor radio channel setting control; measuring means for measuring anelectric field intensity for the radio channel corresponding to theidentification information included in the announcement informationreceived by the announcement information receiving means; and waitcontrol means for comparing an electric field intensity measured by themeasuring means with a preset threshold level, and designating a radiozone to which the radio channel lowest in the hierarchy is assigned as await zone in which to receive the communication service, on thecondition that the electric field intensity measured by the measuringmeans exceeds the preset threshold level.
 3. The mobile communicationsystem as claimed in claim 2, wherein said announcing means comprisesmeans for adding, in the announcement information, preset thresholdvalues individually provided for the radio zone formed by the radio basestation to which the announcing means belongs and the overlapping radiozones and small-scale radio zones, resulting in a hierarchy thatcorresponds to the hierarchy of overlapping zones, and said wait controlmeans employs the threshold values added to the announcement informationby the announcing means in making comparisons with the electric fieldintensity.
 4. The mobile communication system as claimed in claim 2wherein announcing means comprises means for adding a relative valueindicating the preset threshold value for the zone formed by the radiobase station to which the announcing means belongs, in the form of adifference with respect to a reference value for the threshold value,and said announcement information receiving means includes means fordetermining the relative value added to the announcement information, inrelation to the radio zone in which the announcement information isreceived, and said wait control means compares the electric fieldintensity measured by the measuring means with a sum of the referencevalue and the relative value determined by the announcement informationreceiving means in relation to the radio zone in which the electricfield intensity is measured.
 5. The mobile communication system asclaimed in claim 2, wherein said announcing means comprises means foradding relative values indicating the preset threshold values for theradio zone formed by the radio base station to which the announcingmeans belongs and the overlapping radio zones and small-scale radiozones, in the form of differences with respect to a reference valuecommon to the threshold values, resulting in a hierarchy thatcorresponds to the hierarchy of overlapping zones, and said wait controlmeans compares the electric field intensity with a sum of the relativevalue and the reference value.
 6. The mobile communication system asclaimed in claim 2, wherein said mobile station comprises zonedetermination means for performing a cyclic measurement of the electricfield intensity of the radio zones in which the mobile station can belocated, comparing a measured electric field intensity with a loweracceptance value by which an entry into the radio zone is enabled,stopping processes of measurement and comparison when it is found thatthe former exceeds the latter, and selecting the associated radio zoneas a candidate in which the announcement information receiving means isto receive the announcement information.
 7. The mobile communicationsystem as claimed in claim 2, wherein said wait control means comparesthe electric field intensity measured by the measuring means with thethreshold value in the descending order in the hierarchy of the radiozones subject to the measurement, and designates the radio zone forwhich it is found that the former exceeds the latter as a wait zone. 8.The mobile communication system as claimed in claim 6, wherein saidmeasuring means comprises means which omits a measurement of the radiozone selected by the zone determination means and substitutes thereforthe electric field intensity measured by the zone determination means.9. A mobile communication system comprising: a plurality of radio basestations forming one or a plurality of radio zones and one or aplurality of small-scale radio zones, resulting in a hierarchy ofoverlapping zones, and effecting a radio channel setting control inaccordance with a predetermined procedure; and a mobile stationaccessing one of the radio zones formed by the respective one of theplurality of radio base stations, in accordance with a predeterminedprocedure, and receiving communication service via the accessed radiozone, each of the plurality of radio base stations comprising:announcing means for transmitting announcement information whichincludes identification information for identifying the one or theplurality of radio zones and the one or the plurality of small-scaleradio zones, via the radio channel assigned to the radio zone formed bythe radio base station to which the announcing means belongs, theidentification information being arranged in the announcementinformation according to respective positions in the hierarchy ofoverlapping zones, the mobile station comprising: announcementinformation receiving means for receiving the announcement informationtransmitted by the announcing means, in accordance with the procedurefor radio channel setting control; measuring means for measuring anelectric field intensity for the radio zone corresponding to theidentification information included in the announcement informationreceived by the announcement information receiving means; and waitcontrol means for comparing an electric field intensity measured by themeasuring means with a preset threshold level, and designating, as await zone in which to receive the communication service, a radio zonelowest in the hierarchy of overlapping zones on the condition that theelectric field intensity measured by the measuring means exceeds thethreshold level.
 10. A mobile communication system comprising: aplurality of radio base stations forming one or a plurality of radiozones and one or a plurality of small-scale radio zones, resulting in ahierarchy of overlapping zones, and effecting a radio channel settingcontrol in accordance with a predetermined procedure; and a mobilestation accessing one of the radio zones formed by the respective one ofthe plurality of radio base stations, in accordance with a predeterminedprocedure, and receiving communication service via the accessed radiozone, each of the plurality of radio base stations comprising:announcing means for transmitting announcement information whichincludes identification information for identifying radio channels forthe one or the plurality of radio zones and the one or the plurality ofsmall-scale radio zones, via the radio channel assigned to the radiozone formed by the radio base station to which the announcing meansbelongs, the identification information being arranged in theannouncement information according to respective positions in thehierarchy of overlapping zones, the mobile station comprising:announcement information receiving means for receiving the announcementinformation transmitted by the announcing means, in accordance with theprocedure for radio channel setting control; measuring means formeasuring an electric field intensity for the radio channelcorresponding to the identification information included in theannouncement information received by the announcement informationreceiving means; and wait control means for comparing an electric fieldintensity measured by the measuring means with a preset threshold level,and designating one of the radio channels, which is assigned to theradio zone lowest in the hierarchy and for which the control means hasdetermined that the electric field intensity measured by the measuringmeans exceeds the preset threshold level, as a radio channel via whichto receive the communication service.
 11. A mobile communication systemcomprising: a plurality of radio base stations forming one or aplurality of radio zones and one or a plurality of small-scale radiozones, resulting in a hierarchy of overlapping zones, and effecting aradio channel setting control in accordance with a predeterminedprocedure; and a mobile station accessing one of the radio zones formedby the respective one of the plurality of radio base stations, inaccordance with a predetermined procedure, and receiving communicationservice via the accessed radio zone, each of the plurality of radio basestations comprising: announcing means for transmitting announcementinformation which includes identification information for identifyingthe one or the plurality of radio zones and the one or the plurality ofsmall-scale radio zones, via the radio channel assigned to the radiozone formed by the radio base station to which the announcing meansbelongs, the identification information being arranged in theannouncement information according to respective positions in thehierarchy of overlapping zones, the mobile station comprising:announcement information receiving means for receiving the announcementinformation transmitted by the announcing means, in accordance with theprocedure for radio channel setting control; measuring means formeasuring an electric field intensity for the radio zone correspondingto the identification information included in the announcementinformation received by the announcement information receiving means;and wait control means for comparing an electric field intensitymeasured by the measuring means with a preset threshold level, anddesignating, as a wait zone in which to receive the communicationservice, a radio zone identified by the identification information to belowest in the hierarchy of overlapping zones, on the condition that theelectric field intensity measured by the measuring means exceeds thethreshold level.
 12. A mobile communication system comprising: aplurality of radio base stations forming one or a plurality of radiozones and one or a plurality of small-scale radio zones, resulting in ahierarchy of overlapping zones, and effecting a radio channel settingcontrol in accordance with a predetermined procedure; and a mobilestation accessing one of the radio zones formed by the respective one ofthe plurality of radio base stations, in accordance with a predeterminedprocedure, and receiving communication service via the accessed radiozone, each of the plurality of radio base stations comprising:announcing means for transmitting announcement information whichincludes first identification information for identifying a radiochannel assigned to the radio zone formed by the radio base station towhich the announcing means belongs, as well as including secondidentification information identifying the radio zones and thesmall-scale radio zones which overlap the radio zone formed by the radiobase station to which the announcing means belongs, via the radiochannel assigned to the radio zone formed by the radio base station towhich the announcing means belongs, the second identificationinformation being arranged in the announcement information according torespective positions in the hierarchy of overlapping zones, the mobilestation comprising: announcement information receiving means forreceiving the announcement information transmitted by the announcingmeans, in accordance with the procedure for radio channel settingcontrol; measuring means for measuring an electric field intensity forthe radio channel corresponding to the identification informationincluded in the announcement information received by the announcementinformation receiving means; and wait control means for comparing anelectric field intensity measured by the measuring means with a presetthreshold level, determining the radio channel which is identified bythe associated second identification information, if available, to havea lowest hierarchical order, and designating, as a wait zone in which toreceive the communication service, the radio zone to which thedetermined radio channel is assigned, on the condition that the electricfield intensity measured by the measuring means exceeds the thresholdlevel.
 13. A mobile communication system comprising: a plurality ofradio base stations forming one or a plurality of radio zones and one ora plurality of small-scale radio zones, resulting in a hierarchy ofoverlapping zones, and effecting a radio channel setting control inaccordance with a predetermined procedure; and a mobile stationaccessing one of the radio zones formed by the respective one of theplurality of radio base stations, in accordance with a predeterminedprocedure, and receiving communication service via the accessed radiozone, each of the plurality of radio base stations comprising:announcing means for transmitting announcement information whichincludes first identification information for identifying a radiochannel assigned to a radio zone formed by the radio base station towhich the announcing means belongs, as well as including secondidentification information identifying the radio zones and thesmall-scale radio zones which overlap the radio zone formed by the radiobase station to which the announcing means belongs, over the radio zoneformed by the radio base station to which the announcing means belongs,the second identification information being arranged in the announcementinformation according to respective positions in the hierarchy ofoverlapping zones, the mobile station comprising: announcementinformation receiving means for receiving the announcement informationtransmitted by the announcing means, in accordance with the procedurefor radio channel setting control; measuring means for measuring anelectric field intensity for the radio zone corresponding to theidentification information included in the announcement informationreceived by the announcement information receiving means; and waitcontrol means for comparing an electric field intensity measured by themeasuring means with a preset threshold level, determining the radiozone corresponding to the radio channel which is identified by theassociated second identification information, if available, to have alowest hierarchical order, and designating the determined radio zone asa wait zone in which to receive the communication service on thecondition that the electric field intensity measured by the measuringmeans exceeds the threshold level.
 14. A mobile communication systemcomprising: a plurality of radio base stations forming one or aplurality of radio zones and one or a plurality of small-scale radiozones, resulting in a hierarchy of overlapping zones, and effecting aradio channel setting control in accordance with a predeterminedprocedure; and a mobile station accessing one of the radio zones formedby the respective one of the plurality of radio base stations, inaccordance with a predetermined procedure, and receiving communicationservice via the accessed radio zone, each of the plurality of radio basestations comprising: announcing means for transmitting announcementinformation which includes a hierarchical (equal or subordinate) orderof the radio zone formed by the radio base station to which theannouncing means belongs with respect to the overlapping radio zones andsmall-scale radio zones, and which also includes identificationinformation for identifying radio channels assigned to the radio zoneformed by the radio base station to which the announcing means belongsand the overlapping radio zones and small-scale radio zones, via theradio channel assigned to the radio zone formed by the radio basestation to which the announcing means belongs, the mobile stationcomprising: announcement information receiving means for receiving theannouncement information transmitted by the announcing means, inaccordance with the procedure for radio channel setting control, forextracting the identification information from the announcementinformation, and for determining the hierarchy of the radio zones towhich the radio channels identified by the identification informationare assigned; measuring means for measuring an electric field intensityfor the radio channel corresponding to the identification informationobtained by the announcement information receiving means; and waitcontrol means for comparing an electric field intensity measured by themeasuring means with a preset threshold level, and designating a radiozone to which the radio channel lowest in the hierarchy is assigned as await zone in which to receive the communication service, on thecondition that the electric field intensity measured by the measuringmeans for the radio channel lowest in the hierarchy exceeds the presetthreshold level.
 15. A mobile communication system comprising: aplurality of radio base stations forming one or a plurality of radiozones and one or a plurality of small-scale radio zones, resulting in ahierarchy of overlapping zones, and effecting a radio channel settingcontrol in accordance with a predetermined procedure; and a mobilestation accessing one of the radio zones formed by the respective one ofthe plurality of radio base stations, in accordance with a predeterminedprocedure, and receiving communication service via the accessed radiozone, each of the plurality of radio base stations comprising:announcing means for transmitting announcement information whichincludes a hierarchical (equal or subordinate) order of the radio zoneformed by the radio base station to which the announcing means belongswith respect to the overlapping radio zones and small-scale radio zones,and which also includes identification information for identifying theradio zone formed by the radio base station to which the announcingmeans belongs and the overlapping radio zones and small-scale radiozones, over the radio zone formed by the radio base station to which theannouncing means belongs, the mobile station comprising: announcementinformation receiving means for receiving the announcement informationtransmitted by the announcing means, in accordance with the procedurefor radio channel setting control, for extracting the identificationinformation from the announcement information, and for determining thehierarchy of the radio zones corresponding to the identificationinformation; measuring means for measuring an electric field intensityfor the radio zone corresponding to the identification informationextracted by the announcement information receiving means 14g; and waitcontrol means for comparing an electric field intensity measured by themeasuring means with a preset threshold level, and designating a radiozone lowest in the hierarchy determined by the announcement informationreceiving means as a wait zone in which to receive the communicationservice, on the condition that the electric field intensity measured bythe measuring means for the radio zone lowest in the hierarchy exceedsthe preset threshold level.
 16. A mobile station comprising:announcement information receiving means for receiving announcementinformation including orders of priority assigned to radio zones formedby a plurality of radio base stations, the reception by the announcementinformation receiving means being conducted according to a descendingorder of preset traffic distribution and in accordance with a radiochannel setting control procedure; wait means for determining whetherthe radio zone associated with the order of priority included in theannouncement information received by the announcement informationreceiving means satisfies a criteria adapted for the radio channelsetting control procedure, and for designating the radio zone for whichan affirmative answer is given as a wait zone; and communication controlmeans which receives communication service from the radio base stationforming the radio zone designated by the wait means.
 17. A mobilecommunication system comprising: a plurality of base stations formingrespective radio zones that overlap each other; a mobile stationtransportable between said radio zones; wherein each of said pluralityof base stations having: announcing means for sending announcementinformation including an order of priority of said plurality of basestations to the mobile station located in one of said radio zones, andsaid mobile station having: a control means for selecting a base stationfrom among said plurality of base stations, to which a request for amessage channel is to be issued, based on the order of priority of saidplurality of base stations included in the announcement informationtransmitted from said plurality of base stations, rather than based onan order of respective received electric field intensities provided bythe plurality of base stations and being equal to or greater than apredetermined received electric field intensity.
 18. The mobilecommunication system as claimed in claim 17, wherein said mobile stationfurther comprises: announcement information receiving means forreceiving the announcement information including the order of priorityof said plurality of base stations and transmitted from said pluralityof base stations; and transmission means for issuing a request for amessage channel to the base station selected by said control means. 19.The mobile communication system as claimed in claim 18, wherein saidtransmission means includes first transmission means for issuing arequest for a message channel to the base station selected by thecontrol means when a call is originated.
 20. The mobile communicationsystem as claimed in claim 18, wherein said transmission means includessecond transmission means for issuing a request for a message channel tothe base station selected by the control means when a call is incoming.21. The mobile communication system as claimed in claim 18, wherein saidtransmission means includes third transmission means for transmitting arequest for a communication to the base station selected by the controlmeans when a message channel is switched from one to another in theevent of a handover of a call.
 22. The mobile communication system asclaimed in claim 17, wherein said mobile station further comprises:storage means for storing the announcement information; measuring meansfor measuring a reception level in reception-level determining channelsin a descending order of priority of said plurality of base stations,based on the announcement information stored in said storage means andincluding the order of priority and based on information relating to thereception-level determining channels.
 23. The mobile communicationsystem as claimed in claim 22, wherein said control means includesdetermining means for determining whether the reception level in areception-level determining channel is equal to or exceeds apredetermined level that enables a request for a message channel. 24.The mobile communication system as claimed in claim 17, wherein saidannouncing means includes first arranging means for ordering theannouncement information so as to arrange information relating toreception-level determining channels in a descending order of priority.25. The mobile communication system as claimed in claim 17, wherein saidannouncing means includes second arranging means for ordering theannouncement information so as to couple information relating to eachreception-level determining channel to an order of priority associatedtherewith.
 26. A mobile station for use in a mobile communicationsystem, comprising: control means for selecting a base station fromamong a plurality of base stations, to which a request for a messagechannel is to be issued, based on an order of priority of said pluralityof base stations included in announcement information from saidplurality of base stations, rather than based on an order of respectivereceived electric field intensities provided by the plurality of basestations and being equal to or greater than a predetermined receivedelectric field intensity.
 27. The mobile station as claimed in claim 26,further comprising: announcement information receiving means forreceiving, from said plurality of base stations, the announcementinformation including the order of priority of said plurality of basestations; and transmission means for transmitting a request for amessage channel to the base station selected by said control means. 28.The mobile station as claimed in claim 27, wherein said transmissionmeans includes first transmission means for issuing a request for amessage channel to the base station selected by the control means when acall is originated.
 29. The mobile station as claimed in claim 27,wherein said transmission means includes second transmission means forissuing a request for a message channel to the base station selected bythe control means when a call is incoming.
 30. The mobile station asclaimed in claim 27, wherein said transmission means includes thirdtransmission means for transmitting a request for a communication to thebase station selected by the control means when a message channel isswitched from one to another in the event of a handover of a call. 31.The mobile station as claimed in claim 26, further comprising: storagemeans for storing the announcement information; measuring means formeasuring a reception level in reception-level determining channels in adescending order of priority of said plurality of base stations, basedon the announcement information stored in said storage means andincluding the order of priority and based on information relating to thereception-level determining channels.
 32. The mobile station as claimedin claim 31, wherein said control means includes determining means fordetermining whether the reception level in a reception-level determiningchannel is equal to or exceeds a predetermined level that enables arequest for a message channel.
 33. A base station forming a radio zonethat overlaps radio zones formed by other base stations of a pluralityof base stations in a mobile communication system; comprising:announcing means for sending announcement information including an orderof priority of said plurality of base stations constituting the mobilecommunication system to a mobile station located in one of the radiozones, a sending base station being selected by a mobile station fromamong the plurality of base stations, to which a request for a messagechannel is to be issued, based on the order of priority of the pluralityof base stations included in the announcement information, rather thanbased on an order of respective received electric field intensitiesprovided by the plurality of base stations and being equal to or greaterthan a predetermined received electric field intensity.
 34. The basestation as claimed in claim 33, wherein said announcing means includesfirst arranging means for ordering the announcement information so as toarrange information relating to reception-level determining channels ina descending order of priority.
 35. The base station as claimed in claim33, wherein said announcing means includes second arranging means forordering the announcement information so as to couple informationrelating to each reception-level determining channel to an order ofpriority associated therewith.
 36. A mobile station for use in a mobilecommunication system including a plurality of base stations whichrespectively transmit announcement information including an order ofpriority of said plurality of base stations, said mobile stationcomprising: control means for selecting a base station from among theplurality of base stations, to which a request for a message channel isto be issued, based on said order of priority of said plurality of basestations included in said announcement information from said pluralityof base stations, rather than based on an order of respective receivedelectric field intensities provided by the plurality of base stationsand being equal to or greater than a predetermined received electricfield intensity.
 37. A mobile communication system comprising: aplurality of base stations forming respective radio zones; and a mobilestation, the mobile station comprising: a receiver receiving priorityinformation about the radio zones from one of the plurality of basestations; and a controller selecting a radio zone from among the radiozones based on the priority information received by the receiver.